Los Angeles County firefighters were responding to a gas line explosion in Castaic on Saturday, which prompted the California Highway Patrol to close a portion of the 5 Freeway and the Fire Department to order residents to shelter in place.

The Fire Department received reports of the explosion about 4:20 p.m. near Ridge Route Road and Pine Crest Place. There were no injuries, said Fire Captain Brian Kight.

CHP closed all lanes of the 5 Freeway at 5:12 p.m. for an unknown duration.

A landslide in Castaic has ruptured an underground gas line.

A landslide in Castaic has ruptured an underground gas line near Northlake Hills Elementary.

(KNN.NEWS)

The shelter-in-place order, issued at 5:40 p.m., spans much of Castaic and advises residents to close all doors, windows and vents, and shut off HVAC systems.

By 6 p.m., the gas company had shut off both sides of the gas line, but firefighters and a hazmat task force continued to respond to a residual leak.

The cause of the explosion is unknown.

This is a developing story and will be updated.