Californian politicians on Saturday criticized Washington's latest threat to impose tariffs on goods imported from Mexico at a Democratic convention.

Delivering a speech in front of thousands of Democrats and 14 presidential candidates at California Democratic Party Convention in San Francisco, California Governor Gavin Newsom blasted US President Donald Trump's vow to escalate tariffs on goods imported from Mexico step by step until authorities there stop migrants from entering the United States illegally.

Newsom said that no state had more to lose economically from the policy than California, a top trading partner with Mexico.

As one of the biggest trading partners with Mexico, California imported about 44 billion US dollars worth of Mexican goods and exported 30 billion US dollars worth of goods to the southern neighbor last year.

"This is a tax on the American people," Newsom said. "I hope he comes to his senses."

California Senator Kamala Harris, the first speaker among those presidential candidates at the convention, also accused Trump of taxing Americans by initiating trade tensions against other countries.

In a surprise Twitter announcement last week, Trump said that on June 10, "the United States will impose a 5% Tariff on all goods coming into our Country from Mexico, until such time as illegal migrants coming through Mexico, and into our Country, STOP. The Tariff will gradually increase until the Illegal Immigration problem is remedied."