Democratic White House contenders Bernie Sanders and Michael Bloomberg stepped up their attacks on each other on Monday, with Sanders accusing the media mogul of trying to buy the election and Bloomberg saying the senator and his fervent supporters were hurting the party.

Sanders compared the former New York mayor with Republican President Donald Trump, saying both were billionaires trying to use their wealth to bend a corrupt political system.

"Mr. Bloomberg, like anyone else has a right to run for president. He does not have a right to buy the presidency!" Sanders told thousands of supporters at a rally in Richmond, near San Francisco, who booed vehemently at the mention of Bloomberg's name.