The new casino on the banks of the Potomac and in the shadow of the nation’s capital filled to overflowing on its first full day of operations Friday, giving an early indication that the $1.4 billion investment could yield a big payoff for Prince George’s County.

Enthusiasm for the MGM National Harbor casino resort caused traffic backups off the Capital Beltway when the doors opened for the first time late Thursday and again during the day Friday. By midafternoon, new arrivals were delayed at the door until other gamblers and gawkers departed.

“It looks awesome,” said Jeremy Moore, a government contractor from Annandale, Va., who met his wife playing poker in Atlantic City. “This is so much closer to D.C.”

Lashawn Williams said she liked the open layout that provided access to shops and restaurants without requiring people to pass through the casino.

“There may be people who don’t want to gamble — who want to eat or see a show,” Williams said. In the gambling hall, “you have to spend money to win, and I’m not into that.”

The Washington Post was given an exclusive tour of the new MGM National Harbor before its grand opening on Dec. 8. (Ashleigh Joplin/The Washington Post)

Jaweda Howard, a friend who drove up from Richmond with Williams, looked around and concluded that the developers “did a good job.”

Howard said she helped open two casinos in Mississippi that couldn’t compare to the MGM.

“This is definitely more upscale,” said Howard, who was dressed in a stylish houndstooth jacket accented with a matching hat. “It’s inviting — everything is nice.”

Williams, who grew up not far from where National Harbor now sits, said she was impressed with how the area has grown.

“I moved when this was all just woods, and now look at it,” she said.

A county that is home to more people than the city of San Francisco, Prince George’s has for decades been the least favored of the three counties wrapped around Washington. The other two — Fairfax and Montgomery — easily drew high-end merchants, developers and corporations.

But the casino, and the sprawling National Harbor’s shops, hotels and condominiums that preceded it, seem to symbolize Prince George’s revival.

County Executive Rushern L. Baker III (D) called the opening a “watershed moment,” and Maryland Gov. Larry Hogan (R) said it would “have a transformational impact on this region” and Prince George’s.

MGM officials said more than 50,000 people had visited the resort by noon Friday, and later in the day they allowed newcomers into the building only as others left. They expected a weekend crush and urged those with hotel or dinner reservations to arrive early and those who lacked reservations to postpone visiting the resort until well after the grand opening weekend.

“Was it more than we expected? Yes. Was it more than we were prepared to handle? No,” said casino spokesman Gordon Absher. “It was handled quickly, safely and professionally. We are learning lessons. We are making appropriate adjustments.”

With the casino expected to attract 25,000 or more people daily, just what that new volume might mean to the region during two normally congested rush hours caused concern.

When the doors opened to the public at 10:30 p.m. Thursday — 30 minutes early because of the crowds and cold — hordes of would-be gamblers rushed inside.

By 11:30, the casino had reached capacity — about 9,000 — and officials were not admitting additional people. Some frustrated patrons tried to push their way in.

Friday started relatively smoothly. At about 2 p.m., casino officials said that the facility had again reached capacity and additional visitors would be permitted to enter only when others left.

At one point Thursday night, a fight broke out on the casino floor when a man allegedly made unwanted advances toward the female friend of two other men. MGM officials said the instigator was treated for cuts to his face and taken to a hospital.

The chairman of the commission that oversees liquor licenses in Prince George’s County was arrested on drunken-driving charges Thursday night outside the casino after he was in a crash involving two other vehicles, police said.

Charles W. Caldwell III, 72, was charged with DUI, reckless driving and related traffic offenses in connection with the crash, which occurred shortly after the casino’s grand opening, said Cpl. Lamar Robinson, a spokesman for Prince George’s County police.

Absher blamed some of the traffic issues on unfamiliarity with roads and the parking facilities.

“There is a lot of newness,” he said. “Is this weekend going to be crowded? Absolutely. There are going to be a lot of locals who want to come experience it.”

Just how much of a draw the casino will be is the question of the hour, as MGM National Harbor became the sixth gambling house to open in Maryland. Once restricted to Nevada and, later, Atlantic City, there now are dozens of casinos across the country, including those in Pennsylvania and West Virginia.

Edward Aperson of Spotsylvania, Va., took a look around Friday and decided that he preferred the Rocky Gap Casino Resort in Flintstone, Md.

“It’s the traffic. City, traffic — it’s too much hassle,” he said as he surveyed the casino floor. “At Rocky Gap, there’s a beautiful lake — we can camp. It’s more natural.”

In addition to the nearly 4,000 jobs created, the $1.4 billion casino resort is projected to generate between $40 million and $45 million a year in tax revenue for the county — and millions more for the state.

In the food court, friends Jeff Guarini and Phil Dickson were just finishing an early dinner — sandwiches from the deli.

They aren’t big gamblers but were curious to see what a $1.4 billion casino looked like inside. Dickson, a real estate agent in the District, has been to other MGM properties in Las Vegas and was curious about the food offerings.

The men were impressed but not blown away. The service, however, was warm and welcoming, they said.

“I could see myself coming back for a show or event,” Dickson said. Guarini, a consultant visiting from New York, thought he might try his luck at the craps tables.

When the doors opened Thursday night, nearly every machine in the 125,000-square-foot casino was taken almost immediately.

By early afternoon Friday, there were dozens on the waiting list to grab a seat in the poker room. One prospective player said the wait was at least an hour.

The casino, nine miles south of the U.S. Capitol, sits on 23 acres. Maryland officials, marking the opening, noted the building’s architecture as a gateway landmark just off the Capital Beltway.

But MGM aimed for the glamour of Las Vegas and Hollywood.

Actress Sarah Jessica Parker and the celebrity chefs José Andrés, Bryan and Michael Voltaggio, and Marcus Samuelsson, who have restaurants in the resort, posed for selfies as politicians and corporate officials mingled during the open house Thursday.

In addition to numerous county, state and regional elected officials, VIPs sighted included former House speaker John A. Boehner, former RNC chairman and Maryland lieutenant governor Michael Steele and CNN host Wolf Blitzer.

Parker chose the casino as the site for her first stand-alone boutique. During the pre-opening hours for VIPs, she knelt to personally help a shopper try on a pair of $350 Italian-made shoes as a line of curious customers watched.

The resort has already booked Bruno Mars, Cher, Sting and Ricky Martin for concerts in its 3,000-seat theater, which will also feature comedy shows and boxing matches.

Also at the resort is a day spa and a large collection of art by local and international artists, several of whom attended Thursday’s opening festivities.

Then there’s the gambling: The casino will be open 24 hours a day and has more than 3,300 slot machines, 124 gaming tables and 39 poker tables.

Some industry analysts have asked whether the markets in Maryland and on the East Coast are saturated. Others say there is still room for growth in a state where casinos have yet to reach their revenue projections.

“Is gaming vibrant enough to take some more? Yes,” said Richard Clinch, who tracks the gambling industry as director of economic development at the University of Baltimore’s Jacob France Institute. “I think MGM creates a market because it is a national-level operator. It is one of the elite operators of casinos.”

That’s why, officials say, MGM could be a driving force in attracting international visitors. Although the casino is expected to attract gamblers from across the Washington region, MGM executives say their goal is to draw people from across the continental U.S. and worldwide.

Wanda Walker, a retiree from nearby Cheltenham, arrived just after noon with a $10 free-play coupon in her pocket. After months of seeing construction, she was eager to get a look inside.

“It’s nice,” she said as she stood in the conservatory, which was decorated in gold and white for the holiday season.

She said it was a quick drive for her and her two friends — one of whom was playing hooky from work. They found parking right away. It was a pleasant surprise.

“I saw on the TV last night it was a mess,” Walker said.

Having the casino open almost in her back yard was like having a little bit of Vegas nearby. But as far as how it compares with other area offerings?

“We’ll see,” she said. “I have to get a look around.”

Lynh Bui and Arelis Hernández contributed to this report.