The BBC cites a statement from the British government that says Islamist militants in eastern Algeria abducted foreigners in a "terrorist incident" at the Amenas gas production facility.
The field there is operated by a joint venture between BP, Statoil and Algerian state-owned energy company Sonatrach.
The British broadcaster reports that at least one person was killed in the attack.
"Statoil's emergency response organization is now mobilized, and we are now working to get an overview of the situation," the company said in a statement. "Our main focus is the safety of the employees at the facility."
The company said it employed 20 people at the facility. It added that Algerian authorities were in charge of the situation at the local level.
The incident follows a decision by the French government to send military forces to Mali, which shares its northern border with Algeria.
The nationalities of those abducted during the attack are unclear. Statoil said 10 Norwegians are employed at the facility.
There was no immediate statement available from BP or Sonatrach.