OTAY WILDERNESS, Calif.—Firefighters June 3 were battling a wildfire that crossed over the Mexico border from San Diego County.

The blaze erupted for unknown reasons around 12:35 p.m. June 1 near Buttewig Canyon in the South Slope of the Otay Mountain Wilderness and border area, according to an incident report from Cal Fire.

The spread has reached 250 acres in the U.S., with 60 percent containment, and 150 acres in Mexico, Cal Fire said on social media Monday morning.

Firefighters will continue to work on increasing containment throughout the day, Cal Fire reported.

There are 60 personnel assigned to the fire, including five engines, two hand crews, two water tenders, and three unnamed resources.