COPENHAGEN -- A Norwegian Navy frigate carrying a crew of 137 was rammed by a tanker while in a harbour on the country's west coast Thursday, tearing a large hole in its side, the military said.

Eight people on the KNM Helge Instad were slightly injured -- two of whom were taken to a nearby hospital -- in the 4 a.m. accident in Sture, north of Bergen, said Rear Adm. Nils Andreas Stensoenes, the head of Norway's Navy.

The crew were evacuated amid fears the vessel would sink. The ship, which had recently taken part in the vast NATO drill Trident Juncture in Norway, is "strongly listing," Stensoenes told a news conference Thursday afternoon. The frigate was lying in the water almost on its side with its stern under the water.

The Maltese-flagged tanker, Sola TS, was not damaged and its 23-man crew remained on board. The shipping site Sysla reported that the tanker had been loaded with crude oil and was on its way to Britain.

Stensoenes said the cause of the accident was not clear and the Navy would wait for the findings of Norway's Accident Investigation Board. Earlier reports had said a towboat was also involved in the accident, but Stensoenes denied this.

Some 10,000 litres of helicopter fuel from the frigate's tanks leaked into the sea, Johan Marius Ly of the Norwegian Coast Guard said. The fuel was expected to evaporate quickly.

The 134-meter (442-foot) long frigate, built in Spain in 2009, has a helipad platform on its stern.

Stensoenes said the frigate had been pushed by towboats into shallow waters where it could not sink fully. "We are in a security phase for the time being," he added. He declined to comment on what would happen to the weapons on board the ship.

The frigate is part of a NATO fleet in the Atlantic and the alliance has been informed of the accident, he told reporters.

Norway's largest oil and gas company, Equinor, formerly known as Statoil, said it shut down non-emergency activities at the Sture terminal where the collision occurred "as a precautionary measure."

The Accident Investigation Board added that because the tanker is Maltese-registered, the Marine Safety Investigation Unit (MSIU) of Malta will also participate in the investigation.