A major gasoline reservoir in Libya's Zawiya, west of Tripoli, caught fire and collapsed on Monday after what authorities said was an attack by unknown perpetrators.
The National Oil Corporation (NOC) said the tank contained about 4.5 million litres of gasoline.
The reservoir is located at the second-largest oil refinery in Libya, with a refining capacity of 120,000 barrels per day.
"This evening, tank number 402-T, belonging to the Brega Oil Company and used for storing gasoline, was directly targeted, resulting in a severe fire before the tank completely collapsed," the NOC said in a statement.
Brega said in a statement that firefighters were working to contain the blaze, adding that "cooling operations are underway for adjacent tanks to prevent the fire from spreading".
The NOC condemned similar attacks in past days in Zawiya, including two drone attacks on a naphtha reservoir and a water desalination plant over the weekend.
The NOC declared a state of emergency and called for an investigation.
Separately, a Libyan parliamentary panel condemned the attack and called for stronger protection of oil installations.
"The House of Representatives' Energy and Natural Resources Committee condemns in the strongest terms the criminal attack targeting the Zawiya Refinery, one of the most vital facilities in the oil and gas sector that is a cornerstone of the national economy," it said in a statement.
Libya has the most abundant oil reserves in Africa but has been divided ever since it was plunged into war during the ouster in 2011 of former leader Muammar Gaddafi.
Two governments are currently vying for power: the UN-recognised administration in Tripoli led by Prime Minister Abdulhamid Dbeibah and a rival in the east backed by military commander Khalifa Haftar.
In a statement, the Tripoli-based government said Dbeibah held a meeting earlier in the day with key officials, including the interior minister and the chiefs of some armed groups in the capital, "to follow up on the latest security developments".
Dbeibah "stressed the need to deal firmly with any transgressions or actions that threaten security or harm vital facilities and installations", the statement said.
