"I'm running for president because it's time for new leadership, because it's time for new energy and it's time for a new commitment to make sure that the opportunities that I've had are available to every American," Julian Castro told cheering supporters on Saturday.

Castro, who could end up being the only Latino in what is shaping up to be a crowded Democratic field, officially kicked off his campaign with a rally in his home town of San Antonio, where he was mayor for five years.

The 44-year-old ex-housing secretary and grandson of a Mexican immigrant became the second Democrat to formally enter the race, after former Maryland representative John Delaney.

Senator Elizabeth Warren of Massachusetts has also started an exploratory committee for president, and four other Democratic senators are taking steady steps toward running.

Hawaii Representative Tulsi Gabbard, the first Hindu elected to Congress, is planning a bid too.

Castro was raised by a local Latina activist. After a brief career in law, he was elected mayor of the nation's seventh-largest city at 34.

It was not long before Democrats nationally embraced him as a star in the making, particularly one from Texas, where a booming Hispanic population is rapidly changing the state's demographics and improving the party's fortunes.

Castro delivered the keynote speech at the 2012 Democratic National Convention.

Two years later, Obama picked him to lead the Department of Housing and Urban Development.

Australian Associated Press