News of the arrests came as al-Qaida in Iraq claimed responsibility for the bombings.
"A number of suspects were arrested and a number of cars were seized in connection with the terrorist attacks," a Jordanian security official told the country's state-run Petra news agency.
"The investigation with the suspects is under way," the unnamed source added, without revealing the exact number or identities of those arrested.
At least 57 people died and up to 200 were injured in the near-simultaneous explosions at three hotels in Amman.
The blasts which occurred at the Radisson SAS, Grand Hyatt and Days Inn hotels, with most of the casualties reported to be Jordanian nationals.
Another Jordanian security source told AFP on Thursday that six vehicles were seized by the authorities soon after the attacks "including two that have Iraqi licence plates".
The public security department also asked photographers "who were at the sites of the terrorist attacks to hand in their films so that they could be used in the investigation".
Police have appealed to the public
for film of the blast sites
Jordanian police said it "did not receive any information ahead of the terrorist attacks".
Deputy Prime Minister Marwan 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.
The casualty figures show the dead included at least 15 Jordanians, five Iraqi nationals, three Chinese, a Saudi, a Syrian, a Palestinian and an Indonesian, while the bodies of 30 people had yet to be identified.
Israel radio reported that an Israeli businessman was among the dead.
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
Security officials have said they suspect the explosions were caused by suicidebombers.
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.
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."
An Iraqi-linked al-Qaida group
has claimed responsibility
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.
Following Wednesday's explosions, 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 - 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.
In Iraq meanwhile government spokesman Leith Kubba condemned the Amman bombings, saying they showed that countries in the region had to stand together in the fight against terrorism.
Jordan's Queen Rania visited the
injured at an Amman hospital
Kubba also expressed the hope that these attacks would "spark a healthy reaction among Jordan's public opinion which until yesterday was supportive of the Takfiris (Muslim extremists) and of Saddam Hussein loyalists".
A senior Iraqi political leader suggested the Amman bombings required a regional response.
"We weren't really surprised by these attacks," said Jawad al-Maliki, deputy leader of Prime Minister Ibrahim Jaafari's Dawa party.
"They prove that the terrorism which rages in Iraq has also become a real threat to other countries, including those which have closed their eyes on what is going on in our country."
In a separate development, al-Qaida in Iraq also claimmed responsibility for Thursday's suicide bombing on a restaurant in Baghdad which killed 31 people, according to a statement posted on the Internet.