SAN ANTONIO • Mr Julian Castro, the telegenic former mayor of San Antonio, Texas, and Obama-era Cabinet member, launched his bid to become the nation's first Hispanic president last Saturday, emphasising a message of hope and diversity at a time when Americans are locked in angry debate over immigration and border security.

"I am a candidate for the president of the United States," Mr Castro, 44, told a crowd in San Antonio's historic Guadalupe Plaza, during a speech that frequently invoked the immigrant heritage that brought his family to the US from Mexico.

Often called a rising star in the Democratic Party, Mr Castro, who was Mr Barack Obama's housing secretary, and the youngest member of that Cabinet, is expected to be part of a diverse field of candidates eager to challenge President Donald Trump.

At a time when the federal government has been partly shut down over Mr Trump's demand for funds to build a wall on the Mexican border, Mr Castro sounded a contrasting message.

He said San Antonio, a city that is nearly two-thirds Hispanic, "represents America's future: diverse, fast-growing, optimistic".

"Yes, we must have border security, but there is a smart and humane way to do it. And there is no way in hell that caging children is keeping us safe," he said.

"We say no to building a wall and say yes to building community," he added, to roars from the crowd.

Mr Castro's twin brother, Joaquin, who introduced him last Saturday, is a congressman.

The two rode to the event together on the same bus line that once took them to public school.

Mr Castro is the third candidate with a Latino background to seek the presidency in recent years, after two Republicans, Senator Ted Cruz of Texas and Mr Marco Rubio of Florida, unsuccessfully faced Mr Trump in that party's 2016 primary campaign.

AGENCE FRANCE-PRESSE