The intense fighting involved two influential militias from western Libya, local media reported.
No casualties or motive for the fighting were immediately apparent, but it is the latest violence to rock the country as two rival prime ministers vie for power.
After a 2011 revolt toppled longtime dictator Mouammar Kadhafi, political infighting to fill the power vacuum has plagued oil-rich Libya.
Last month, politician Fathi Bashagha attempted to seize power by force, sparking pre-dawn clashes between armed groups supporting him and those backing interim premier Abdulhamid Dbeibah.
Dbeibah was appointed under a troubled UN-led peace process early last year to lead a transition to elections set for December 2021, but the vote was indefinitely postponed.
In February, parliament appointed Bashagha, a one-time interior minister, to take over, arguing that Dbeibah’s mandate had ended.
But Dbeibah has insisted he will only relinquish power to an elected administration.