Armed groups traded fire with heavy weapons in the centre of Tripoli, injuring at least nine people and paralysing the Libyan capital, residents and the Red Crescent said on Friday.
"Our team... rescued nine people injured in the indiscriminate firing," said the Libyan Red Crescent, which has set up a field hospital on a roundabout on the fringes of the urban combat zone.
There was no official casualty toll from the clashes which raged most of Thursday night and resumed the following day after a truce collapsed.
The fighting between two rival armed groups in eastern Tripoli erupted after one accused the other of kidnapping four of its members, the Tripoli-based news agency LANA reported.
It said families trapped in the conflict zone of Abu Slim were appealing to the authorities to intervene to halt the violence which has closed down the city centre.
Mediators had secured an overnight ceasefire but fighting later resumed, LANA said.
"Two apartments in housing blocks on the airport road were hit by rockets. I can see columns of smoke," local resident Nuria al-Mosbahi told AFP.
Other residents said tanks and trucks mounted with heavy anti-aircraft guns had criss-crossed the zone, leaving behind several burnt-out cars.
In the absence of a statement from the Government of National Accord which is based in Tripoli, a leading political figure, Aguila Saleh, issued a condemnation of the violence.
"What's happening in Tripoli is a terrorist and criminal act which destabilises... citizens and the institutions of state," he said.
Libya has been submerged in chaos since the fall and killing of longtime dictator Muammar Gaddafi in a NATO-backed 2011 armed uprising.
Rival political authorities and militias have since been vying for control of territory and Libya's oil wealth.