Crews battling 22 tenacious wildfires in drought-stricken California rushed in reinforcements Tuesday and girded for weather that could ignite more fast-spreading blazes.

More than 10,000 firefighters are now tackling blazes that have forced thousands to flee their homes and burned large swaths of land in the most populous US state.

The biggest blaze, called the Rocky Fire, has drawn in 3,200 firefighters. Valiant efforts by fellow crews meanwhile contained the Point Fire in Shasta County and the Pines Fire in Los Angeles County, CAL FIRE said.

"Tinder dry conditions from the drought continue to allow wildfires to burn at an explosive rate," said the California Department of Forestry and Fire Protection, or CAL FIRE.

The state is bringing in extra people from southern California to the hard-hit north, making already deployed firefighters work overtime and canceling days off, CAL FIRE spokesman Daniel Berlant told MSNBC.

Resources from out of state, such as the Colorado state air reserve, are also being rushed in, Berlant said.

In Washington, President Barack Obama was briefed on uncontained wildfires in California and elsewhere in the west, White House spokesman Josh Earnest said, praising the bravery of the firefighters.

"These are selfless individuals and we owe them a debt of gratitude for putting their lives on the line to fight these fires and protect their fellow Americans," he said.

Thunderstorms that can bring lightning, the source of many fires this summer, but virtually no water, were forecast.

And while temperatures cooled over the weekend, they are expected to rise again Wednesday, followed by more thunderstorms on Thursday, CAL FIRE said in a statement.

Many of the fires are actually made up of dozens of smaller lightning fires, Berlant said.

- 'Historically fast' -

"Right now definitely conditions are dry. We are continuing to see the effects of the drought as wildfires can more easily spark and then they're going to spread at these historically fast rates," he said.

The week-old Rocky Fire prompted evacuations as it swept through Colusa, Lake and Yolo counties north of Sacramento, the state's capital, in the north of the state.

More than 13,000 people have been forced to flee homes threatened by Rocky, CAL FIRE said.

Only 20 percent under control, Rocky has burned through more than 67,000 acres (27,000 hectares), destroying 50 structures, about half of them homes.

Berlant said late Monday that the fire ripped through the forests at breakneck speed, with firefighters struggling to keep apace.

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

At least 142,000 acres of land have burned so far, according to figures provided by the state.

California is in the throes of a record-breaking drought, with much of the state completely parched and residents asked to make major cutbacks in water use.

In the northern part of the state some forests were completely engulfed by the infernos, and several stretches of highway were forced closed.

In areas where fires had been put out, charred cars were all that was left behind on some roads, and trees were left smoldering on the blackened earth.

A state of emergency was issued Friday and the California National Guard has been called in, underlining the scale of the threat facing the western state.

A firefighter from South Dakota, Dave Ruhl, 38, was killed Thursday while fighting the Frog Fire in the Modoc National Forest outside Alturas, California.