Anti-aircraft gunfire has rattled the sky over Tripoli overnight. It follows the first attacks on Libyan air defences from western allies enforcing the UN-backed no-fly zone.
Explosions and machine-gun fire were also heard in the Libyan capital.
It came hours after Operation Odyssey Dawn got underway – the biggest international military intervention in the Arab world since the Iraq war.
French planes fired the first shots, reportedly destroying military vehicles in the east.
US officials say more than 110 Tomahawk cruise missiles have been fired from British and American ships.
They have been aimed at coastal targets and air defence sites.
Reports say British jets have also carried out long-range bombing raids.
The Pentagon said it was too early to determine the success of the strikes.
“The goals of these initial operations are essentially twofold”, said US Vice Admiral William Gortney. “First, to prevent further attacks by regime forces on Libyan citizens and opposition groups, especially in and around Benghazi. And second, to degrade the regim’s capability to resist the no-fly zone we are implementing under that United Nations resolution.”
The operation begun by French planes now involves Italy and Canada as well as Britain and America.
What each side is saying about the impact varies wildly: the US claims Libyan air defences have been “severely disabled”.
Libyan state television claims the raids have killed 48 people and wounded 150 in civilian areas of several cities.