Nexen Energy is shutting down its Long Lake oilsands operations south of Fort McMurray in response to an emergency regulatory order.

Nexen estimated the shutdown process would take up to two weeks as it suspends pipeline operations and attempts to demonstrate to the Alberta Energy Regulator (AER) that its pipelines are safe.

The provincial regulator gave the order as part of an ongoing investigation into a large spill discovered in July. Five million litres of of bitumen, sand and oil leaked from a pipeline at the facility.

"The suspension order requires the company to shut in 95 pipelines, which is about a quarter of the total number of pipelines at the Long Lake site," Bob Curran, an AER spokesperson, said in a statement.

"Our focus remains the same: the company must provide us with assurance that the lines in question can be operated safely."

Nexen, the Canadian subsidiary of Chinese state-owned CNOOC, says the pipelines impacted by the suspension order comprise the majority of the facility's infrastructure required for operations.

"Nexen is complying with the AER's suspension order," said spokesperson Diane Kossman in an email. "We're providing them with necessary documentation, suspending our pipelines and shutting down our Long Lake oilsands operations.

"We're managing the risks associated with safely shutting down this complex and integrated facility," she added.