SACRAMENTO, CALIFORNIA (REUTERS) - United States President Joe Biden on Monday (Sept 13) renewed his push for significant investments to combat climate change as he visited California during a three-state western US tour and took an aerial tour of areas hit by one of the country's worst fire seasons.

The trip is aimed at highlighting the devastation caused by a warming planet, pushing for more resources to tackle the issue and touting the environmental initiatives that are part of the infrastructure bills his administration is pushing.

Mr Biden will also campaign for fellow Democrat Gavin Newsom, who is battling to maintain his governorship in California's recall election on Tuesday.

Mr Biden toured the California Governor's Office of Emergency Services in Sacramento with Mr Newsom, where he addressed emergency operations officials and said parents are not just worried for their children over Covid-19 but whether they can also breathe the air.

"We have to act more rapidly, we have to act more firmly, and we have to act more broadly... It really is a matter of what the world will look like," Mr Biden said.

He then boarded his Marine One helicopter, which flew over a parched landscape hazy with smoke from the relentless wildfires. Patches of black in the landscape showed areas where the fires had been put out.

The Caldor Fire in California, which had threatened the Lake Tahoe resort area, has charred more than 219,000 acres and destroyed more than 1,000 homes and other structures since it erupted in the Sierra Nevada range about 100km east of Sacramento on Aug 14.

As of Monday, firefighters had carved containment lines around 67 per cent of the fire's perimeter. It is the second-largest blaze in the state this year, behind the Dixie Fire, which has scorched more than 960,000 acres and destroyed 1,300-plus buildings farther north in the Sierras since it began in mid-July. That wildfire ranks as California's second-largest on record.

Earlier in the day, Mr Biden visited the National Interagency Fire Centre in Boise, Idaho, a hub designed to coordinate resources on wildfires - and held a briefing with state and local officials.

In Boise, the President said fire season in the US is starting earlier each year and that this year alone, 44,000 wildfires in the country had consumed 5.4 million acres - an area roughly the size of New Jersey.

"Thank God, thank God we have you," Mr Biden told firefighters in the room. He pledged to help federal firefighters make at least US$15 (S$20) an hour and said he is committed to raising the pay gap for firefighters who protect federal wildlands.

"The reality is we have a global warming problem, a serious global warming problem," Mr Biden said, pegging the economic damage from extreme weather events last year at US$99 billion.

White House principal deputy press secretary Karine Jean-Pierre said on Monday that one in three Americans is affected by the increasing frequency of extreme weather events and that Mr Biden's message on his first trip to the US West Coast as President would be that the "climate crisis is in code red".

The White House said late on Sunday that Mr Biden had approved US disaster funding to help California amid the Caldor Fire. He ordered other federal assistance earlier this month after declaring the situation an emergency.

Mr Biden will head to Long Beach, California, to take part in an event with Mr Newsom, an ally who is fighting to survive a Republican-led recall. Mr Biden's presence, the day before polls close, is meant to help mobilise Democrats to vote and secure Democratic leadership of the nation's most-populous state. Democrats outnumber Republicans in California and recent polling shows a majority of likely voters opposing the recall, but Mr Biden and Mr Newsom are not taking anything for granted.

Vice-President Kamala Harris, a former US senator from California, campaigned for Mr Newsom last week and painted the recall, which is backed financially by state and national Republican groups, as part of a broader Republican effort to expand conservative restrictions on voting, abortion and LGBTQ rights.

On Tuesday, Mr Biden will turn his focus to infrastructure during a stop in Denver where he will tout multitrillion-dollar legislation he is seeking to repair US roads and bridges along with a swathe of other domestic policy priorities.