"The In Salah Gas asset in Krechba was hit by explosive munitions fired from a distance," Statoil said in a statement.
"Statoil is working on getting an overview of the situation, but has so far no information about anybody being injured during the attack," it said.
Algeria's energy infrastructure is heavily protected by the army especially since the 2013 Islamist militant attack on the In Amenas gas plant, also operated by BP and Statoil, during which 40 oil workers were killed.
Stateoil said in a statement that the gas facility was hit by explosive munitions from a distance.
"In the early morning, three or four rocket propelled grenades hit a central processing facility, there were no casualties or damage reported," an industry source.
The Algerian army were controlling the area and pursuing the attackers. BP said in a statement that the facility had been closed down as a safety precaution.
BP said in a statement that the facility had been closed down as a safety precaution.
According to BP's website, In Salah started production in 2004 from three fields Krechba, Teguentour and Reg. In February, it announced the start up of development of the Gour Mahmoud, In Salah, Garet el Befinat and Hassi Moumene fields, to bring output to 9 billion cubic metres a year.
The 2013 In Amenas attack was carried out by militants linked to veteran Algerian jihadist Mokhtar Belmokhtar, who U.S. forces say may have been killed in an air strike in Libya last year. Al Qaeda has denied he was killed.
Belmokhtar's group Al Murabitoun or "Those who sign in Blood" has been blamed for several attacks across the region. Al Qaeda in the Islamic Maghreb has also claimed recent attacks in the Ivory Coast, Mali and Burkina Faso.
Attacks and bombings in Algeria, one of Europe's main gas suppliers, have become rarer since the North African country emerged from a 1990s war with Islamist fighters that killed around 200,000 people.
But Al Qaeda in the Islamic Maghreb, and its affiliates, and fighters allied with Islamic State, are active in remote pockets of the country, mainly in the desert south and the mountains east of the capital Algiers.
Algeria and other North African countries are also increasingly worried about the rapid expansion of Islamic State over their border in Libya, where the militant group has taken over the city of Sirte and attacked oilfields and ports.