Up to 200 people are also reported to have been injured in the blasts, which occurred at the Radisson SAS, Grand Hyatt and Days Inn hotels on Wednesday night in the Jordanian capital.
Jordanian Deputy Prime Minister Marwan Muasher said on state television that most of those killed were Jordanians.
Speaking on state television, Muashir said the country's land borders had been sealed and "more measures will be understaken soon". He did not elaborate.
Iraq's al-Qaida said it had carried out the bomb attacks, in a statement posted on the internet.
"A group of our best lions launched a new attack on some dens ... After casing the targets, some hotels were chosen which the Jordanian despot turned into a backyard for the enemies of the faith, the Jews and crusaders," the statement on a website usually used by the group, said on Thursday.
"Let the tyrant of Amman know that his protection...for the Jews has become a target for the mujahideen and their attacks, and let him expect the worst," it added.
"A group of our best lions launched a new attack on some dens ..."
al-Qaida in Iraq's internet statement
A security official told Aljazeera that the explosions could have been caused by human bombers.
The official, speaking on condition of anonymity because he was not authorised to address the media, said the dead included at least three Asians, possibly Chinese.
Two senior Palestinian officials, too, have been killed in the blasts, said the Palestinian envoy to Amman on Thursday.
According to the Associated Press, the first explosion occurred at 8.50pm local time (1850 GMT) in or near the lobby of the Grand Hyatt.
A second blast followed shortly afterwards, hitting a wedding hall at the Radisson.
Aljazeera reporter Yassir Abu Hilala said the third blast hit a nightclub at the Days Inn.
Security has been beefed up
across Jordan after the blasts
He added that police had arrested several people at the scene of the Radisson hotel explosion.
Abu Hilala said police were also on the lookout for a car with Iraqi licence plates.
Muasher said two human bombers attacked the Grand Hyatt and the nearby Radisson SAS. The Days Inn attack was carried out by an explosives-laden vehicle that blew up outside the hotel after failing to cross a police line.
Most of the victims at the Radisson were Jordanians attending a wedding banquet in a ground-floor reception hall, where a man strapped with explosives infiltrated the crowd.
"We thought it was fireworks for the wedding; but I saw people falling to the ground," said Ahmed, a wedding guest who did not give his surname. "I saw blood. There were people killed. It was ugly."
All the hotels are located in the commercial Jabal Amman district and are frequented by Western business travellers and diplomats.
Aljazeera's reporter said that Jordan had recently received warnings of possible attacks.
He added that the Israeli embassy is close to the Days Inn, although police do not believe the embassy was a target.
An Iraqi-linked al-Qaida group
has claimed responsibility
"Journalists were driven away and police confiscated their tapes as a security measure," Abu Hilala said.
All foreign embassies in Amman have been cordoned off following the explosions, security sources told Aljazeera.
Following the attacks, security was beefed up across the capital, especially around hotels and diplomatic missions.
Several armed policemen and cars were patrolling the streets of Amman, where Prime Minister Adnan Badran declared Thursday a national holiday - apparently in order to allow tightened security measures to take hold.
King Abdullah II - who cut short an official visit to Kazakhstan and was returning home on Wednesday night - condemned the attacks as "criminal acts committed by a deviant and misleading bunch" and said they would not sway Jordan from its battle against terrorism.
"The hand of justice will get to the criminals who targeted innocent secure civilians with their cowardly acts," he said in a statement carried by the official Petra news agency.
King Abdullah: The hand of justice
will get to the criminals
Arson experts arrived at the Hyatt shortly after the explosion to inspect the scene and ensure that there were no other bombs, according to an AP reporter on the scene.
Black smoke rose into the night and the wounded stumbled out of the hotels. The stone entrance of the Hyatt was completely shattered.
An AP reporter saw seven bodies and many wounded being carried out on stretchers.
A spokesperson for the Hyatt said the hotel had been evacuated and police had cordoned off the area and assumed control of the hotel.
Jordan, a key ally of the US, had largely escaped the terror attacks that have hit other parts of the Middle East, and its sleepy capital, Amman, is viewed as a haven of stability in the region.
But Jordan has not been entirely immune: On 19 August, fighters fired three Katyusha rockets at a US navy ship docked at the Red Sea resort of Aqaba, narrowly missing it and killing a Jordanian soldier.