The state of California in the U.S. is now literally a ball of wildfires, worsened by droughts and high temperatures. The federal website U.S. Drought Monitor on Thursday said 100 per cent of the state is now in one of the three worst stages of drought.

On Thursday, firefighters continued to mobilise and dispatch more air support to control the seven fires raging north of San Diego where thousands were forced to flee and evacuate their homes.

The U.S. Drought Monitor, for the first time in its 14-year history, has classified the whole state of California in a "severe drought."

Already building for the past few years, the California drought peaked this 2014. When April came in, all of the state was in a drought, where 70 per cent was in "extreme" or "exceptional" drought, the two highest stages.

"Things are not trending in the right direction," Mark Svoboda, a scientist at the National Drought Mitigation Center, told Climate Central.

In May, the situation became worse. One hundred per cent of the state now is in the three worst stages of drought. Exceptional drought, the highest stage, occurs from Los Angeles to San Francisco and inland to the foothills of the Sierra Nevada mountains.

On Wednesday, seven fires broke out between San Diego and San Clemente where experts said will continue to be intensified by the heat wave that hit the state this week.

"The heat will exacerbate and accelerate the impact concerns that come with higher demand (for water) and increased fire risk during such heat waves," Svoboda said.

Daniel Berlant, a Cal Fire spokesman, said the department has already extinguished 1,400 wildfires across the state, which is more than twice the average number for this time of year alone.

"It starts with the drought," Berlant told the Los Angeles Times. "The grass, the brush and the trees -- not only in San Diego County, really across California -- are really dry."

"Fire season from 2013 rolled right into 2014 and continues with no end in sight," he added.

"It's really awful, unprecedented," CNN meteorologist Jennifer Gray said. "We have never seen California this dry before. So this wildfire season could be one of the worst in history."

"A lot of these fires would be a lot more manageable and not nearly as damaging if not for the drought," Danny Richards, Hutchinson County's emergency management coordinator, said.