The closure only adds to the growing chaos in Libya, whose internationally recognised government has been driven out of the capital by an alliance led by forces from the city of Misrata, which has installed a rival government and parliament.
In the main eastern city of Benghazi, five pro-government soldiers were killed and 28 wounded on Saturday while fighting Islamists, lifting the death toll from three weeks of clashes to 300, Reuters quoted medics as saying.
The protesters at Hariga were part of a state security oil force that has gone on strike over pay several times this year.
“There is a sit-in from security guards who say they have not been paid,” Reuters quoted one Libyan official, who asked not to be named, as saying. “We are trying to solve the issue.”
A tanker had been waiting for three days to lift oil from Hariga, located in Tobruk, but the guards did not allow it to do so, the official told the news agency.
The port was only open for fuel imports and the exports of refinery products, which are marginal, he added.
The closure will lower Libya’s output to about 500,000 bpd or even less, based on previous published figures. The state-run National Oil Corporation has not given a production update for a month.
Libya’s oil industry had already been struggling with the closure of the southerly El Sharara oilfield, which used to pump at least 200,000 bpd, because of attacks by gunmen.
A senior oil worker at the field, who asked not to be named, said authorities hoped to restart the field within three to four days if the security situation allowed it.
But an officer in the Petroleum Facilities Guard (PFG) at the oilfield said gunmen had attacked El Sharara again on Friday.
“There was fighting yesterday between PFG (forces) of the field and invaders, resulting in one wounded PFG member and three killed invaders,” he said.
But he said the PFG members had then withdrawn, leaving the remote field to the gunmen. No more details were immediately available.
Some Libyan websites have said the attackers are supporters of the group that seized the capital in August, but Reuters has been unable to confirm this.
The senior oil worker said the El Sharara closure would not affect the Zawiya refinery connected to the field as tanks there had stocks for 17 days. NOC could get fresh supplies from the south-westerly El Feel field or via the Es Sider oil port, he added.
The 120,000 bpd-refinery supplies the capital Tripoli and western Libya with gasoline.
Libya’s oil industry had been recovering in the past few months from a wave of protests at ports and oilfields that had lowered output to 100,000 bpd in the first half of the year. Output hit 900,000 bpd in September.