The 137 people on board the KNM Helge Ingstad frigate, which was returning from NATO's Trident Juncture exercises, were evacuated after the collision with the Sola TS tanker, the military said.
The warship is now in danger of sinking, while the tanker, named the Sola TS, is slightly damaged and did not spill oil.
'It took on a lot of water and there is a real danger that it will sink where it is, ' an official for the Sola rescue centre told AFP.
Spilling from the frigate is a slick of what is reportedly light oil and helicopter fuel, although Norwegian NRK reports there's no immediate threat to the environment after oil barriers were put in place on Thursday morning.
The tanker, with 23 crew, suffered damage well above the waterline. Eight injured crew members were taken off as well as the other 129 on board.
The main phase of the Trident Juncture 2018 training - in which more than 40,000 troops from 30 member countries and North Atlantic Treaty Organisation partners participated - took place from October 25 to November 7 in Norway and its surroundings.
Sola TS tanker crashed into Helge Ingstad, tearing a large hole in its side, near the Sture terminal in Oygarden at around 4 a.m (0300GMT) on Thursday. The police, which investigate marine accidents in Norway, have cordoned off the area around the stricken frigate for fear of explosions.
One Norwegian news outlet reports that according to tracking data, the frigate's geolocation system was turned off at the time of the collision, noting, however, that the armed forces of Norway have neither confirmed nor denied that.
Heavy shipping traffic is the norm at Sture, where a quarter of all oil produced in oil-rich Norway is processed.
There are no reports as to when the damaged navy vessel, which is part of NATO's Atlantic fleet, will be salvaged.