A Nexen pipeline has failed, spilling millions of litres of bitumen, produced water and sand at its Long Lake project about 35 kilometres southeast of Fort McMurray.

Nexen officials say fail-safe mechanisms designed to detect breaches did not work and the leak was located by a contractor on Wednesday afternoon. It is not known when the pipeline burst occurred and it's possible the leak had been spilling its contents over an extended period of time.

The spill is considered one of the largest oil sands spills in Canada in recent memory, as five million litres has spewed, enough to fill two Olympic sized swimming pools.

Nexen says the affected area is about 16 thousand square metres, mostly along the pipeline’s route. The site has been deemed to be under control but the emulsion has apparently spilled into some muskeg.

Peter Murchland with the Alberta Energy Regulator says the concern is public, wildlife and environmental risks associated with a pipeline spill but there’s currently no impact to animal or human life.

"We have no indication that there's any risk to public health or public safety," explains Murchland.  "Certainly, with regard to wildlife, there's no imminent risk to wildlife issues due to the wildlife protection plan."

"We'll work closely with the operator to ensure the environment that's impacted, in this case 40 metres by 400 metres, is actually contained."

Nexen says all necessary steps and precautions have been taken, and Nexen will continue to utilize all its resources to protect the health and safety of our employees, contractors, the public and the environment.

The double-layered pipeline was installed last year at Nexen's Long Lake site.

"We're deeply concerned that this incident has happened," said Ron Bailey, Nexen's senior vice president. "We need the investigation to go through its normal course to fully understand this."

"We're concerned about the impact here and we'll be looking at our operating procedures, our design procedures."

A berm has been constructed to help contain the spill and a temporary road has been built to allow cleanup crews access to the site of the burst.

The Alberta Energy Regulator will not impose penalties, if any, on Nexen until its investigation into the pipeline spill is complete. A timeline for the completion of the investigation has not been released.