Kieran Cain was at the playground with his two children when he heard what sounded like a “sonic boom.” He looked up to see an airplane, black smoke in the sky — and hunks of metal hurtling down.

He and his family rushed for cover in a gazebo, he told CNN. They watched the wreckage fall as close as a couple of blocks away. Photographing the damage later, Cain told the network, he passed a house with a hole in its roof. At another, he said, a giant ring had struck a man’s RV, bounced off the garage and crashed down just in front of the porch.

“It was raining metal,” Cain said the man told him.

And yet the plane kept going.

The United Airlines flight, Honolulu-bound with more than 200 passengers, returned to Denver International Airport shortly after takeoff Saturday afternoon following an engine failure, strewing debris at least a mile wide in yards and a park where children play, authorities said. Police in Broomfield, Colo. — about a half-hour north of Denver — sent out a “code red” urging about 1,400 people to check their yards for fallen wreckage.

But miraculously, officials said, not a single injury has been reported, and Flight 328 made it back safely to the airport.

Broomfield Police spokeswoman Jennifer McIntyre told The Washington Post that the park would have been much busier — with crowds of children playing soccer — before the coronavirus pandemic. “And we actually had a nice day today, almost into the 50s, but luckily the park wasn’t that populated,” she said.

United Airlines confirmed that the flight “experienced an engine failure shortly after departure” but did not elaborate on the potential cause of the breakdown. The Federal Aviation Administration said Saturday that the National Transportation Safety Board will lead an investigation.

The airline said Sunday that it will temporarily ground 24 Boeing 777 aircraft “out of an abundance of caution,” according to a statement.

“Need to turn — mayday,” the pilot on Flight 328 said in a call to air traffic control, his voice betraying little emotion.

United said Saturday evening that all passengers and 10 crew members had left the Boeing 777. Customers were “comfortable and cared for” while the airline prepared another flight, spokesman David Gonzalez said, and most were scheduled to land in Honolulu later in the night. Others who “did not wish to travel with us this evening” were given hotel rooms, he added.

Broomfield Police said they received reports that debris had fallen in “several neighborhoods” about 1:10 p.m. local time. They urged people to call in about debris as patrol officers searched for it and shared a photo of a giant metal ring that crashed into a front yard — the home of the man Cain recalled speaking with on CNN.

Other hunks of the engine wound up on the turf field at Commons Park in Broomfield.

“Given the number of people who are at Commons Park on a weekend day we are beyond grateful that no one was injured,” police tweeted.

McIntyre confirmed that debris went through the roof of at least one house.

Passengers recounted terror onboard.

“I can honestly say I thought we were going to die at one point — because we started dropping altitude right after the explosion,” David Delucia, 47, of Fort Lauderdale, Fla., told the Denver Post. “I grabbed my wife’s hand and said, ‘We’re done.’ ”

Delucia told the newspaper that a fellow passenger took a video that went viral on Twitter after his stepdaughter posted it. It showed orange flames coming out of a rattling engine. It took nearly half an hour to get back to the airport, Delucia said, full of “the worst turbulence you can imagine.”

“What a crazy … experience,” he told the Denver Post from the airport later. “It was nuts — absolutely nuts.”

The family did not immediately respond to The Post’s inquiries.

United did not respond to questions about the video clip, but Broomfield Police shared it on Twitter.

“Unbelievable,” they said.

Meryl Kornfield contributed to this report.