California's Department of Forestry and Fire Prevention (CALFIRE) reported late Monday that "well over 9,000 firefighters" were battling 21 active fires across the western state.

"There are 21 active fires across California, well over 9,000 firefighters battling them. Thousands of lightning strikes have occurred since last week, sparking several hundred small wildfires," CALFIRE said in a statement.

Authorities urged more than 13,000 people to evacuate their homes - some with mandatory orders - as the blazes raged on in drought-stricken California.

'Rocky Fire'

The "Rocky Fire" has been the most difficult to contain, burning through 101 square miles (261 square kilometers) of land, while destroying 50 buildings in the process, half of which were homes.

At least a third of the firefighters deployed across the state are working to contain "Rocky Fire."

"It's the Rocky Fire that continues to really be a fast-moving fire that definitely continues to challenge us today," CALFIRE spokesperson Daniel Berlant told American broadcaster CNN.

"Over the weekend, 20,000 acres burned in just about a five-hour period. That's an unprecedented historical rate of spread," Berlant said.

At least one firefighter has been killed by the blazes, which erupted Wednesday.

Historic drought

California's four-year-long drought has caused major issues for the western state's population.

In May, California Governor Jerry Brown ordered residents to cut water consumption by at least 25 percent, impacting farmers in the process.

Cool weathers are expected to dampen the blazes, although Berlant issued a warning on Monday night that lightning strikes may continue to produce "single fire 'complexes.'"

ls/ (AFP, AP, Reuters)