A series of explosions rumbled across other parts of the city as fighter jets could by heard flying overhead. Fire engines raced through the streets, sirens blaring.
It wasn't clear what was hit or whether there were casualties. Friday is the main day of rest in Libya, with many people off work.
NATO has been ramping up the pressure on Moammar Gadhafi's regime. Though most airstrikes happen under cover of darkness, daytime raids have grown more frequent.
Friday's raids follow a barrage that struck multiple targets late Thursday night.
The fresh strikes blasted the capital as renewed diplomatic efforts to halt Libya's civil war appeared to be gaining momentum, though there are no signs a breakthrough is imminent.
On Thursday, Russia's envoy to Libya met with senior government leaders in Tripoli, but not Gadhafi himself, in an effort to stop the fighting.
Last week, the envoy Mikhail Margelov visited the Libyan rebel stronghold of Benghazi and said that Gadhafi has lost his legitimacy. However, the envoy also said NATO airstrikes are not a solution to Libya's violent stalemate.
Libyan Prime Minister al-Baghdadi al-Mahmoudi said the Libyan government has held a number of "preliminary meetings" with officials based in the eastern rebel-held city of Benghazi. He said the talks took place abroad, including in Egypt, Tunisia and Norway, but he did not provide specifics.
A coalition including France, Britain and the United States launched the first strikes against Gadhafi's forces under a United Nations resolution to protect civilians on March 19. NATO assumed control of the air campaign over Libya on March 31. It's joined by a number of Arab allies.
What started as a peaceful uprising inside Libya against Gadhafi has grown into a civil war, with rebels now holding a third of the country in the east and pockets in the west.
Libya's rebels mark Feb. 17 - four months ago Friday - as the start of their revolution against Gadhafi's more than four-decade rule.
It was on that date that protesters emboldened by Arab uprisings in neighboring Tunisia and Egypt took to the streets in a number of Libyan cities. At least 20 people were reported killed in a crackdown by state security forces.
Fighting between government forces and the rebels had reached a stalemate until last week when NATO launched the heaviest bombardment of Gadhafi forces since the alliance took control of the skies over Libya.