Firefighters have extinguished two fires at oil storage tanks at Libya's Ras Lanuf terminal, but blazes continue at five tanks in the nearby port of Es Sider after attacks this week by Islamic State group (ISIS) militants, a Petroleum Facilities Guards (PFG) spokesman said on Thursday.

Two tanks were hit by shelling this week and the fires spread later.

Spokesman Ali al-Hassi said the PFG remained in control of the area and that there were no clashes on Thursday. The fighting, which began on Monday with a car bombing against a guards' outpost, has left 11 guards dead and more than 40 wounded, he said.

Separately, nearly 50 people were killed on Thursday when a truck bomb exploded at a police training centre in the town of Zliten, east of Tripoli, local officials and hospital sources said.

Both Es Sider and Ras Lanuf have been closed since December 2014. They lie between the city of Sirte, which is controlled by ISIS, and the eastern city of Benghazi.

An oil official based in eastern Libya estimated that the tanks hold up to 460,000 barrels each.

Libya is split between political factions and armed groups competing for power and for the country's oil wealth, nearly five years after the revolt that toppled Libyan leader Muammar Gaddafi.

The OPEC member state's oil output has plunged to less than one quarter of a 2011 high of 1.6 million barrels per day.