Eye witnesses told local media outlets that the HQ was on fire and that the building had been surrounded by security forces. There has been no official confirmation regarding any casualties following the incident.

The security services are looking for gunmen in the building, but our priority is to evacuate the civilians stuck inside," said Ahmed Ben Salem, a spokesman for al-Redaa, a militia that operates as Tripoli's police force. "The situation is under control," he added.

An official for Libya’s National Oil firm who requested to remain anonymous claimed that masked gunmen had exchanged fire with guards and attacked the firm’s HQ. The official said, “I jumped out of the window with other colleagues, and then we heard an explosion.”

This latest attack come just four months after suicide bombers struck the headquarters of Libya's electoral commission, killing 14 in an attack claimed by the Islamic State group.

Libya's vital oil sector has been repeatedly disrupted by violence since a 2011 NATO-backed rebellion that toppled longtime dictator Moamer Kadhafi.

Petrochemical exports had accounted for the vast majority of state revenues under Kadhafi's rule, with production at 1.6 million barrels per day.

But since his regime was overthrown, the output in oil had fallen to about 20 percent of that level, before recovering to more than one million barrels per day by the end of 2017.

Oil producers' cartel OPEC has estimated Libya's oil reserves at 48 billion barrels, the biggest in Africa. Two rival governments and a range of armed groups are struggling for control of Libya and its resources.