Three nearly simultaneous bomb blasts tore through hotels here Wednesday night, killing more than 50 people, wounding at least 110 and sending fear and panic through the streets of the normally tranquil city.

Jordanian authorities immediately shut down many of the capital's main roads and deployed dozens of ambulances, police cars and military vehicles to help evacuate the wounded to a half-dozen overflowing hospitals. The country's land borders were closed about an hour after the attacks.

No group immediately asserted responsibility for the attack, though several government officials said the coordination and execution -- apparently by suicide attackers -- bore the mark of the al Qaeda network.

The explosions came in rapid succession about 9 p.m. Hours afterward, downtown streets were filled with hundreds of people. Some were hotel guests who said they did not know where to go, while others were family members of victims, wandering from hospital to hospital looking for information about their loved ones.

"I carried at least 20 people back and forth to the Jordan Hospital. Everybody was screaming and crying, mothers were confused. . . . I was just shocked," said Marwan Muhammed Hani, 22, a taxi driver who was parked at the Grand Hyatt hotel when a bomb exploded inside.

Each of the blasts targeted a hotel owned by a Western chain. The first bomb killed more than 20 people in the Grand Hyatt, one of the city's largest lodgings, police at the scene said. At the Radisson SAS Hotel, also west of downtown, at least 20 people attending a wedding reception in a banquet room were killed, according to police and hospital officials.

Initial reports suggested suicide bombers on foot were responsible for those two blasts, although police at the scene said a rigged device had been planted in at least one of the hotels. The third blast came when a car detonated in the street outside the Days Inn, police and government officials said.

The death toll was the largest in a hotel bombing since July 23, when attacks on three hotels in the Egyptian resort of Sharm el-Sheikh killed as many as 88 people.

"We still don't know why this was done. Obviously anyone who blows himself up in a wedding hall is not someone who wants the good of his country or the good of any human being," said Jordan's deputy prime minister, Marwan Muasher, speaking to reporters in front of the Radisson. He said that there were 57 deaths as of 11:30 p.m. and that it appeared most of the victims were Jordanians.

Despite its proximity to Iraq, Amman is widely considered one of the Middle East's safest capitals, and luxury hotels have had only minimal apparent security. Drivers could bring cars directly to the front doors of most hotels, and no metal detectors or identification checkpoints were present. Hours after the attacks Wednesday night, however, police closed streets in front of several large hotels and employees checked room keys and waved metal-detecting wands at people entering.

"Things here had gotten very relaxed and soft. No one seemed to care about security procedures," said Jamil Nimri, a Jordanian newspaper columnist, looking at the charred wreckage of the Radisson.

Jordanian security forces have thwarted a number of potentially devastating attacks in recent years. In what became known as the millennium plot, Abu Musab Zarqawi, a Jordanian who is now the most-wanted insurgent leader in Iraq, targeted several tourist sites in the city, including the Radisson, just before New Year's Eve in 1999. Authorities uncovered the scheme and Zarqawi fled the country.

In April 2004, Jordanian officials said they had broken up an attempted chemical attack on the capital that they said could have killed 20,000 people. Police said they foiled another planned attack against hotels and embassies that summer.

This August, Zarqawi's al Qaeda in Iraq group asserted that its fighters had launched Katyusha rockets that narrowly missed a U.S. warship in Jordan's Red Sea port of Aqaba.

"All the fingers for what happened tonight point to al Qaeda and Zarqawi," said Muhammed Arsalan, assistant to the country's parliament speaker, who toured each of the bomb sites Wednesday. "They have been trying for a long time, and we were lucky. But they found a weak point."

Jordanian officials declared that Friday would be a national day of mourning. King Abdullah said on national television that "the hand of justice will reach the perpetrators wherever they are."

In Washington, President Bush said in a statement: "The barbaric acts again demonstrated the terrible cruelty of the terrorists and the great toll they take on civilized society. . . . To the people of Jordan and King Abdullah, we pledge our full support in their efforts to bring the terrorists to justice."

Hotel employees sounded an alarm just after the explosion at the Grand Hyatt, which guests said took place in a ground-floor bar. Guests said they were first directed to a basement shelter and then were handed white blankets and asked to leave the building through emergency exits.

Usama Jabr, 59, an Iraqi physician, said he was visiting Amman for a cardio-thoracic convention and was hoping for some "peace and quiet." He was in the Grand Hyatt's restaurant with some colleagues "when we heard something that sounded like a rocket attack I heard once in Baghdad," he said. "It was a violent explosion. We saw smoke and broken glass, and everyone started to panic. There was a waiter crying and yelling because of cuts in his eyes."

At Jordan Hospital, family members of the victims gathered outside and grew increasingly agitated as police barricaded the doors, refusing to let anyone enter. Twice, wailing women broke through the police lines and charged toward the door, only to be turned away by hospital staff members.

A man speaking on a cell phone fell to his knees and began to shout, "No, no, no!" Friends helped him to his feet and led him to a waiting car.

Ahmed Zerkia, 35, leaned against a car and punched the keys of his cell phone with trembling fingers. His brother Aref, 50, had been in the wedding party, he said, along with dozens of other family members.

"My cousin called me and said, 'Your brother is dead.' But I want to know for sure, so I came here," said Zerkia, wearing a pinstriped gray suit, his eyes welling with tears. "He's my big brother. He's like my father. I try and try but I cannot reach anyone in his family."

Researcher Julie Tate in Washington contributed to this report.

A body is removed from the Grand Hyatt in Amman after the first of three blasts, minutes apart, at hotels in the Jordanian capital. A suicide bomber on foot was suspected in the Grand Hyatt attack, which killed more than 20. An injured man is helped away from the Grand Hyatt hotel in Amman after the bombing there. Many of the city's hospitals were crowded with casualties.