Saboteurs on Monday blew up a pipeline that supplies gas to Israel, the official MENA news agency reported, just hours before the first election since Hosni Mubarak was ousted.
Masked gunmen planted explosives under the pipeline west of the town of El-Arish in the north of the Sinai peninsula, MENA said.
A second blast occurred seconds later around 100 metres away from the first explosion, a security official told AFP.
Witnesses said they saw the masked men driving away from the area just minutes before the blasts, which sent raging flames into the sky, visible from miles away.
Emergency services were rushed to the scene to try to control the blaze, the official said, adding that there were no immediate reports of casualties.
The attack – the ninth of its kind this year – came just hours before polling was due to start in landmark parliamentary elections.
The pipeline, which carries gas through the Sinai and on to Jordan and Israel, has already been attacked eight times this year, the first during the mass uprisings that drove President Hosni Mubarak from power in February. The last attack was carried out on Friday.
Gas deliveries to Israel, agreed under Mubarak, have come under heavy criticism in Egypt.
Israel generates 40 per cent of its electricity using natural gas, and Egypt provides 43 per cent of its gas supplies.
Egyptian authorities have on several occasions announced measures to step up protection of the pipeline and try to arrest those behind the attacks.
Egyptian gas also covers 80 per cent of Jordan's electricity production demand – 6.8 million cubic metres a day.
Egypt's Sinai region is particularly security sensitive due to tensions with the Bedouin community living there.
Many goods are smuggled to the Palestinian enclave of Gaza through the Sinai, which the Israelis also charge is a rear base for militant attacks against its territory.