California's Gavin Newsom says he will run for governor in 2018
San Francisco Mayor Gavin Newsom at the Web 2.0 Summit (JD Lasica/Flickr)

California's Lieutenant Governor said Wednesday he would run for governor in 2018, staking an early claim to fund-raising and endorsements as the most populous U.S. state faces an unprecedented generational shift in political leadership.

Gavin Newsom made the announcement four years ahead of the election amid ongoing jostling among fellow California Democrats over the state's top three political jobs, all of which will come open in the next several years.

Newsom aims to succeed popular Governor Jerry Brown, who will be 81 when his term ends.

"The reality of running for Governor - even four years from now – in America’s largest, most diverse state demands that I start raising resources now if we’re going to lead a conversation worthy of the 38 million people who live, work, attend school and raise families in the Golden State," Newsom said in a statement emailed to reporters on Wednesday.

A former mayor of San Francisco whose support for same-sex marriage kicked off a tidal wave of social and political change, Newsom is one of several California officials expected to run for higher political office as the state's two U.S. senators and Brown approach retirement.

Last month, U.S. Senator Barbara Boxer, 74, said she would not run for re-election when her term ends in 2016, leading state Attorney General Kamala Harris to get into the race. Newsom declined to run against Harris, who has much the same political base, choosing instead to go after the governor's job.

U.S. Senator Dianne Feinstein, 81, has not said whether she will run again when her term is up in 2018, but if she retires also, a third top job will be open in the state.

Newsom's move may further crowd out former Los Angeles Mayor Antonio Villaraigosa, who has been weighing a run against Harris and is also widely believed to be considering seeking the governorship.

Many Latino leaders have held off endorsing Harris in the race, even though she has the support of the state's Democratic party kingmakers, to see what Villaraigosa will do.

Some in Latino political circles have complained that in the rush to support Harris, Latino candidates including Villaraigosa have been shunted aside.

On Wednesday, the union representing Los Angeles police officers endorsed Harris, her campaign said.

(Reporting by Sharon Bernstein; Editing by Ken Wills)