"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 last 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.
Mediators had secured an overnight ceasefire but fighting later resumed, LANA said.
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"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.
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.