Vehicles are pictured during clashes in south of the capital Tripoli's suburb of Ain Zara. Mahmud Turkia/AFP

Several air strikes and explosions shook the Libyan capital Tripoli overnight, residents said, in an escalation of a two-week offensive by eastern forces on the city held by the internationally recognised government.

A Reuters reporter and several residents said they saw an aircraft circling for more than 10 minutes over the capital late on Saturday, and that it made a humming sound before opening fire on several areas.

An aircraft was heard again after midnight, circling for more than ten minutes before a heavy explosion shook the ground.

It was not clear whether an aircraft or unmanned drone was behind the strike, which triggered heavy anti aircraft fire. Residents had reported drone strikes in recent days, but there has been no confirmation and explosions heard in the city centre this time were louder than in previous days.

A Libyan fighter fires a rocket propelled grenade during clashes in Ain Zara, Saturday. Mahmud Turkia/AFP

Residents counted several missile strikes, one of which apparently hit a military camp of forces loyal to Tripoli in the Sabaa district in the south of the capital, scene of the heaviest fighting between the rival forces.

Authorities closed Tripoli's only functioning airport, cutting air links to a city of an estimated 2.5 million residents. The airport in Misrata, a city 200 km to the east, remained open.

The Libyan National Army (LNA) force loyal to commander Khalifa Haftar started an offensive two weeks ago but has been unable to breach the government's southern defences.

If a drone strike was confirmed this would point to more sophisticated warfare. The LNA has so far mainly used ageing Soviet-made jets from the air force of Muammar Gaddafi, toppled in 2011, lacking precision firepower and helicopters, according to residents and military sources.

Reuters