According to the Fort St. John RCMP, the leak began behind the Credit Union in the alley of 101 Street.
Authorities are still unsure of the cause, but suspect construction within the area may be a factor.
Police were forced to evacuate the Credit Union and clear the area, with the safety of the public the main reason for the evacuation.
Police have now left the scene, with the Fort St. John Fire Department resuming control of the situation.
The Credit Union has since been reopened, with staff and customers allowed back in.