One person has been arrested in connection with a serious fire at a CN Rail building in Prince Rupert, B.C.

The fire burned for hours after breaking out Sunday afternoon. RCMP were called around 4 p.m. PT, and officers soon arrested a young man for suspected arson.

The man remains in custody.

Cpl. Devon Gerrits said the incident isn't believed to be related to recent protests at CN Rail sites across the country, some of which have involved small fires.

"No real motivation as of yet," Cpl. Gerrits said Monday morning.

Around 70 people crowded on a nearby hillside to watch firefighters work to save the large building.

Gerrits said the building, near the Kwinitsa station at the waterfront, had been unoccupied for some time.

The officer said investigators are combing through surveillance footage from the area.

The Prince Rupert Fire Department could not be reached for comment on Monday.