"We are still lacking reliable information concerning nine people", Prime Minister Jens Stoltenberg said.
That number dropped to eight after Norwegian oil group Statoil revealed one of its workers had made it to safety and was being treated in an Algerian hospital for minor injuries.
Twelve employees of Statoil, which operates the gas field with BP and state-run Algerian energy firm Sonatrach, were earlier reported "involved" in the hostage taking.
Stoltenberg said it was too early to judge the Algerian operation to free dozens of hostages from various countries who were seized by Islamists at the In Amenas gas field in retaliation for a French offensive in Mali.
At a separate press conference, Statoil chief Helge Lund said eight other employees — Norwegian and Algerian — who had been at or around the site at the time of the hostage taking, were safe.
BP and Statoil will evacuate "non-essential" staff from its other sites in Algeria, Lund said.