Firefighters on Friday battled a blaze at an oil facility in northern Libya for a second day, an official said, after an assault by jihadists aiming to seize export terminals.
Libya's internationally-recognised government, meanwhile, called for Western air strikes to repel the jihadists.
"Four storage tanks together containing around two million barrels of crude oil are on fire," said a security official in the Ras Lanouf region along Libya's northern coast.
The blaze in one of the tanks is beyond control "and we expect it to collapse at any moment", he said. "We are now working on putting out the fires in the other three tanks."
"The disaster exceeds our capacities," added the official, asking not to be named.
Fighting broke out at dawn on Thursday in Ras Lanouf, the National Oil Corporation (NOC) said.
It said storage tanks filled with crude had caught fire, causing clouds of dense smoke.
It called the situation "catastrophic for the enviroment" and said that nearby high-voltage power lines and electrical towers had also been downed.
State news agency LANA said Islamic State (IS) group jihadists were behind the attack and that the storage tanks belonged to Harouge Oil Operations.
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The company has 13 storage tanks with a combined capacity of 6.5 million barrels at its site, nine kilometres (six miles) from Ras Lanouf port.
An NOC official told AFP a committee has been formed to evaluate the damage.
The attack came two days after a national unity government was formed under a UN-brokered deal aimed at ending political divisions that have seen Libya torn between rival administrations.
A spokesman for Libya's recognised government in the east told AFP it was requesting a "limited intervention" by the international community to "protect oil fields from IS attacks".
Hatem el-Ouraybi said the government wanted "air strikes against IS positions" in Libya.
The government has previously called for an air campaign against IS, like in Iraq and Syria, but world powers are first waiting for rival sides to endorse the unity government.
IS has in recent weeks launched repeated attacks from its stronghold in the city of Sirte on facilities in the "oil crescent" along the country's northern coast.
Libya sits atop estimated oil reserves of 48 billion barrels, the largest in Africa.
But output has slumped since the North African country's longtime leader Moamer Kadhafi was ousted and slain in a 2011 revolution, tipping the country into insecurity and political chaos.