An intruder attacked the husband of US House Speaker Nancy Pelosi with a hammer, fracturing his skull, after breaking into their California home on Friday in search of her.

Paul Pelosi was "attacked at home by an assailant who acted with force, and threatened his life while demanding to see the speaker," Pelosi spokesman Drew Hammill said.

Paul Pelosi, 82 -- who underwent surgery and is recovering in hospital -- was at home alone, as his wife was working in Washington.

San Francisco police said officers found the assailant at the couple's home just before 2:30 am (0930 GMT), where he and Paul Pelosi were scuffling over a hammer.

"The suspect pulled the hammer away from Mr. Pelosi and violently assaulted him with it," San Francisco police chief Bill Scott told reporters.

He named the assailant as 42-year-old David Depape but declined to take questions and offered little further detail.

US media, citing family sources, said the intruder told Paul Pelosi he was going to tie him up and wait for the speaker to get home.

The victim managed to dial 911 while the man was distracted, according to an account given to cable network MSNBC.

Local media had earlier reported that the intruder shouted "Where's Nancy?" during the assault but police told reporters a motive had not yet been determined.

Scott said Depape would be charged with attempted homicide, assault with a deadly weapon, burglary and other felonies.

"Mr. Pelosi was admitted to Zuckerberg San Francisco General Hospital where he underwent successful surgery to repair a skull fracture and serious injuries to his right arm and hands," the speaker's spokesman added.

"His doctors expect a full recovery."

Nancy Pelosi -- who is second in line to the presidency -- and the couple's five children were reported to be returning to San Francisco to be by his side.

President Joe Biden called the Democrat, also 82, to express his support over the "horrible attack" and was praying for her husband, the White House said.

"He is... very glad that a full recovery is expected. The president continues to condemn all violence, and asks that the family's desire for privacy be respected," Biden's press secretary Karine Jean-Pierre said in a statement.

'Disgusted'

The intruder broke in through a sliding-glass door, The Wall Street Journal reported, citing unnamed law enforcement officers, leaving him with wounds to the head and body.

He has taken extreme right-wing positions on social media, including conspiracy theories about Covid-19, one of the officers told the daily newspaper.

With less than two weeks to go before the crucial US midterm elections, members of both parties have sounded the alarm about the potential for political violence.

According to the Capitol Police in Washington, threats against lawmakers have more than doubled since 2017 to nearly 10,000 in 2021.

Members of both parties rallied to support Pelosi on social media, with several suggesting the assault was the inevitable result of an increase in violent political rhetoric.

Adam Kinzinger, a Republican member of the House committee investigating the January 2021 attack on the US Capitol, blamed conspiracy theories spread by Donald Trump and his far-right followers for radicalizing some supporters.

"I want to be clear: when you convince people that politicians are rigging elections, drink babies' blood, etc, you will get violence. This must be rejected," he said of Friday's attack.

Republican House whip Steve Scalise said he was "disgusted" by the attack.

Paul Pelosi was convicted of drunk driving after an accident in May and sentenced to five days in jail.