Los Angeles, Jun 28 (IANS): Two wildfires have erupted in California's Riverside and San Bernardino counties, prompting evacuation of residents, while also threatening multiple structures, officials said.

The fires were reported on Tuesday and they broke out about 48 km apart, reports The Los Angeles Times.

The 'Juniper' fire in Riverside County was reported at around 2.30 p.m. in the 19000 block of Santa Rosa Mine Road, according to Alex Izaguirre, a spokesperson for the Cal Fire/Riverside County Fire Department.

By 5.45 p.m., it had grown to at least 55 acres with 5 per cent containment.

About 100 firefighters were battling the blaze from the air and the ground, including 19 engine companies and four air tankers, Izaguirre said.

It has also prompted mandatory evacuations for residents of 88 homes.

Dubbed the 'Nice' fire, the blaze ignited at 3.09 p.m. in San Bernardino Mentone community near Nice Avenue and Amethyst Street, The Los Angeles Times reported citing the California Department of Forestry and Fire Protection as saying.

It said that the fire was moving slowly, with no structures threatened.

The cause of the two fires are being probed.

The wildfire have erupted as the National Weather Service (NWS) has warned of this summer's first heat wave set to hit Southern California this week.

Temperatures are expected to soar to the triple digits this weekend, and the NWS has advised residents that hot, dry conditions could support rapid fire growth should a blaze ignite.