Heavy explosions were also heard in the capital, Tripoli, late on Sunday.
The raids came as Nato took full command of the whole military operation in Libya, intended to enforce a UN resolution to protect civilians.
Foreign correspondents in Sirte said they heard several loud explosions in the city as aircraft flew overhead.
A rebel spokesman in Benghazi has said Sirte is now in the hands of rebel forces – but there has been no independent confirmation of the claim.
Later, Libyan government spokesman Moussa Ibrahim said three young Libyan men had been killed in an air strike on a fishing harbour near Sirte. There was “nothing military or quasi-military” there, he said.
Libyan officials say more than a week of strikes have killed nearly 100 civilians but this cannot be independently confirmed.
The air strikes, intended to prevent Col Gaddafi’s forces from attacking civilian targets among the uprising against his rule, have allowed rebel forces to push westwards along the coastal highway from their eastern stronghold of Benghazi.
In the last two days a number of coastal communities and important oil installations, including Ras Lanuf, Brega, Uqayla and Bin Jawad, have fallen to the rebels since they took control of Ajdabiya.
Sirte lies about halfway along the coast between Tripoli and and Benghazi. Journalists in the city on Sunday said it was swarming with soldiers.
“We want to go to Sirte today,” rebel fighter Marjai Agouri told Reuters news agency.
“I don’t know if it will happen,” he said outside Bin Jawad with about 100 other rebels armed with rocket launchers, anti-aircraft guns and pickup trucks mounted with machine guns.