Electricity supplies across Iraq have been disrupted after saboteurs attacked a key oil pipeline junction on the Tigris River in northern Iraq.
Thick clouds of black smoke billowed after the blast
Engineers had to shut down a nearby power station in Baiji, fearing that flames would spread there.
The move set off a technical chain reaction which led to power outages across the entire country.
Repeated attacks on Iraq's crucial oil infrastructure have resulted in a loss of revenue estimated at $2bn.
Insurgents struck at about 0300 local time (2200 GMT) at a point where two pipelines ran side-by-side down to the River Tigris.
The attack near Baiji, 250 km (155 miles) north of Baghdad, set off a fire that melted cables and led to the power outage, electricity officials said.
Daylight revealed a huge fire on the riverbank, crude oil pouring down the slope into the river and thick clouds of black smoke.
The flow has now been turned off, but that in effect puts the whole of Iraq's northern oilfield - around the nearby city of Kirkuk - out of action, the BBC's Elizabeth Blunt reports.
Iraq's Minister of Electricity Ayham al-Samarie said engineers and technicians were working to restore power as soon as possible and that 30% of the work had been done.
"Power will be back in the coming hours," the minister said in a statement.
In a separate development, a fire erupted in a pipeline about 60km (40 miles) southwest of Kirkuk, halting exports to Turkey, Iraqi officials said.
Normally Kirkuk oil either goes to the refinery and power station in Baiji itself or continues down the pipeline to Turkey, so the blazes simultaneously hit oil exports, power generation and domestic fuel supplies, our correspondent says.
Iraq has a complicated network of pipelines, and they are designed to provide alternative routes when needed.
Exports to Turkey had already been reduced by an attack on the main pipeline last month, although some oil had been diverted to other routes.
Iraqi Oil Minister Thamer al-Ghadhban meanwhile told fellow OPEC members at a meeting in Vienna that the country's production had now reached 2.5 million barrels of oil a day, two million of them for export.
But it is proving a constant struggle to maintain that figure, our correspondent says.
Iraqi President Iyad Allawi said this week that the saboteurs had already cost Iraq about $2bn in lost revenue.