Fire north of Los Angeles erupts from a few dozen acres to more than 7 square miles in just hours.

A fast spreading wildfire has caused multiple injuries, forced mandatory evacuations and closed California’s main north-south freeway.

The fire started just as a severe heat wave, which is expected to last for several days, hit Southern California.

The Route fire, as it has been named by authorities, began near Castaic, about 40 miles northwest of Los Angeles on Thursday, Aug. 31 around noon, initially burning about 60 acres, according to Cal Fire data.

By 7 p.m. the fire had jumped in size to nearly 5,000 acres, more than seven square miles, with no containment.

Half a dozen firefighters were taken to hospitals suffering from heat related injuries, the Los Angeles Times reported. Temperatures in the area reached 110 degrees during the afternoon. In addition, the area is extremely mountainous.

Mandatory evacuations have been ordered in the area.

The fire has also forced the closure of Interstate Highway 5, the main north-south freeway in the state, forcing detours of hundreds of miles and promising to snarl travel and shipping in the state for days. 

California and much of the western U.S. are expected to see severe hot weather through the Labor Day weekend with temperatures expected to exceed 100 degrees in much of Southern California. 

California’s electrical grid operator has ordered a Flex Alert for Thursday, calling for voluntary electricity conservation “due to continuing extreme temperatures pushing up energy demand and tightening available power supplies.”

Wildfires are a common occurrence throughout California during summer and fall. In recent years they have been made more intense because of sustained drought conditions that have dried out trees and ground cover in much of the state.