Libyan separatists loaded oil onto a North Korean tanker for a second consecutive day on Sunday, ignoring the central government's threats of military action, an industry official said.

The separatists are former rebels who have turned against the interim authorities in the restive North African country after toppling veteran dictator Moamer Kadhafi in the 2011 uprising.

Separatists have been blockading oil terminals in eastern Libya that they had been entrusted with guarding over demands for autonomy in eastern regions and a share in lucrative oil revenues.

On Saturday, they began loading oil onto the Panamanian-flagged "Morning Glory" tanker docked at Al-Sidra terminal.

Prime Minister Ali Zeidan ordered them to stop or else the tanker would be bombed, while Oil Minister Omar Shakmak accused the separatists of an "act of piracy".

On Sunday, Culture Minister Amin al-Habib said Libyan navy ships had been deployed at sea to stop the tanker from leaving port.

"The tanker cannot leave any more, or it will be turned into a pile of metal," he said at a press conference.

The defence ministry also said orders for military action had been issued to the armed forces, the official Lana news agency reported.

The ministry ordered the chief of staff, the navy and the air force "to deal with the tanker that entered Libyan waters without a prior permit from the legitimate authorities," Lana said.

The report came as National Oil Corporation spokesman Mohamed al-Harairi said the Morning Glory was "still inside the harbour and loading is underway".

Harairi said he expected the operation to continue until the end of Sunday, noting that the ship could take up to 350,000 barrels of crude oil.

But he was unable to give details on any plans by the authorities to stop the tanker from leaving the port.

- Plans to intercept ship -

However, military sources said plans were in place to intercept the tanker before it leaves Libya's territorial waters.

Premier Zeidan told a news conference late Saturday that the attorney general had given the order for the ship to be stopped.

"All parties must respect Libyan sovereignty. If the ship does not comply, it will be bombed," he said.

Zeidan said the authorities had told the vessel's captain to leave Libya's waters, but added that armed gunmen on board were preventing him from setting sail.

A spokesman for the self-proclaimed government of Cyrenaica in the east, the political wing of the separatists, had said Saturday that oil exports from Al-Sidra had begun.

"We are not defying the government or the Congress (parliament). But we are insisting on our rights," said Rabbo al-Barassi, who heads the Cyrenaica executive bureau formed in August.

The crisis erupted in July, when security guards at key terminals shut them down, accusing the authorities of corruption and demanding a more equitable distribution of oil revenues.

The situation has become more complicated as self-rule activists have insisted on the right to export.

Oil is a key source of revenue for Libya and following the blockade of terminals production plunged to about 250,000 barrels per day from 1.5 million barrels.