European and US forces unleashed warplanes and cruise missiles against Libyan leader Muammar Gaddafi's troops in the biggest Western military intervention in the Arab world since the invasion of Iraq in 2003.
Libyan state television said 48 people had been killed and 150 wounded in the Western air strikes. It also said there had been a fresh wave of strikes on Tripoli early on Sunday.
There was no way to independently verify the claims.
CBS News on its website said on Sunday that three US B-2 stealth bombers had dropped 40 bombs on a "major Libyan airfield" that was not further identified. A Pentagon spokesman said he had no information about such an attack.
French planes fired the first shots on Saturday in a campaign to force Gaddafi's troops to cease fire and end attacks on civilians. The warplanes destroyed tanks and armoured vehicles near the rebels' eastern stronghold, Benghazi.
Burned out military vehicles lined the main road into Benghazi on Sunday as the rebels advanced back towards the strategic town of Ajdabiyah they lost last week.
One tank had its turret blown off. A tank transporter, tank and an armoured personnel carrier were still smouldering. Fourteen bodies lay in the desert next to the vehicles.
"This is all France ... Today we came through and saw the road open," said rebel fighter Tahir Sassi, surveying the scene.
US and British warships and submarines launched 110 Tomahawk missiles overnight against air defences around the capital Tripoli and the western city of Misrata, which has been besieged by Gaddafi's forces, US military officials said.
They said US forces and planes were working with Britain, France, Canada and Italy in operation "Odyssey Dawn". Denmark said it had four fighter planes ready to join in on Sunday and was awaiting US instructions.
Gaddafi called it a "colonial, crusader" aggression.
"It is now necessary to open the stores and arm all the masses with all types of weapons to defend the independence, unity and honour of Libya," he said in an audio message broadcast on state television hours after the strikes began.
Western air forces were expected to use the coming of daylight on Sunday to assess what damage they had done, and there appeared to be a lull in the aerial bombardment.
China and Russia, which abstained in the UN Security Council vote last week endorsing intervention, expressed regret at the military action. China's Foreign Ministry said it hoped the conflict would not lead to a greater loss of civilian life.
Explosions and heavy anti-aircraft fire rattled Tripoli in the early hours of Sunday. The shooting was followed by defiant shouts of "Allahu Akbar" (God is Greatest) that echoed around the city center.
Libyan state television showed footage from an unidentified hospital of what it called victims of the "colonial enemy". Ten bodies were wrapped up in white and blue bed sheets, and several people were wounded, one of them badly, the television said.
Tripoli residents said they had heard an explosion near the eastern Tajoura district, while in Misrata they said strikes had targeted an airbase used by Gaddafi's forces.
A Reuters witness in the eastern rebel stronghold of Benghazi reported loud explosions and anti-aircraft fire during the night, but it was unclear which side was shooting.
The intervention, after weeks of diplomatic wrangling, was welcomed in Benghazi with a mix of apprehension and relief.
"We think this will end Gaddafi's rule. Libyans will never forget France's stand with them. If it weren't for them, then Benghazi would have been overrun tonight," said Iyad Ali, 37.
"We salute France, Britain, the US and the Arab countries for standing with Libya. But we think Gaddafi will take out his anger on civilians. So the West has to hit him hard," said civil servant Khalid al-Ghurfaly, 38.
Gaddafi seen losing grip on Libya
The strikes, launched from some 25 ships, including three US submarines, in the Mediterranean, followed a meeting in Paris of Western and Arab leaders backing the intervention.
French President Nicolas Sarkozy said the allies had agreed to use "all necessary means, especially military" to enforce the Security Council resolution for an end to attacks on civilians.
"Colonel Gaddafi has made this happen," British Prime Minister David Cameron told reporters after the meeting. "We cannot allow the slaughter of civilians to continue."
Some analysts have questioned the strategy for the military intervention, fearing Western forces might be sucked into a long civil war despite a US insistence, repeated on Saturday, that it has no plans to send ground troops into Libya.
Canadian Prime Minister Stephen Harper suggested that outside powers hoped their intervention would be enough to turn the tide against Gaddafi and allow Libyans to force him out.
"It is our belief that if Mr. Gaddafi loses the capacity to enforce his will through vastly superior armed forces, he simply will not be able to sustain his grip on the country."
But analysts have questioned what Western powers will do if the Libyan leader digs in, especially since they do not believe they would be satisfied with a de facto partition which left rebels in the east and Gaddafi running a rump state in the west.
One participant at the Paris meeting said Clinton and others had stressed Libya should not be split in two. And on Friday, President Barack Obama specifically called on Gaddafi's forces to pull back from the western cities of Zawiyah and Misrata as well from the east.
"It's going to be far less straightforward if Gaddafi starts to move troops into the cities, which is what he has been trying to do for the past 24 hours," said Marko Papic at the STRATFOR global intelligence group.
"Once he does that it becomes a little bit more of an urban combat environment and at that point it's going to be difficult to use air power from 15,000 feet to neutralise that."
Nevertheless Obama has pledged not to deploy ground forces.
"As I said yesterday, we will not, I repeat, we will not deploy any US troops on the ground," Obama told reporters.
France and Britain have taken a lead role in pushing for international intervention in Libya. The US, after embarking on wars in Afghanistan and Iraq, acknowledged on Saturday it was in charge of operations but said it intended to switch to a "coalition command" in the coming days.