Veteran comic actor Jim Carrey has labeled California's governor a "corporate fascist" for ordering tougher rules on mandatory vaccinations, claiming they can poison children.

In an ongoing Twitter rant Wednesday, Carrey insisted he is not against vaccinations as such, but claimed that those advocated by the western US state for schoolchildren contain neurotoxins including mercury.

"All we are saying is, 'Take the neurotoxins out of the vaccines.' Make them toxin free. History will show that that was a reasonable request," Carrey tweeted.

The comments came after Governor Jerry Brown signed a bill Tuesday toughening vaccination requirements for children, following a measles outbreak and outcry across the country.

The new law will require all children to be immunized before entering kindergarten, with exceptions allowed only if a doctor advises against immunization.

Carrey started his series of tweets late Tuesday, saying: "California Gov says yes to poisoning more children with mercury and aluminum in manditory (sic) vaccines. This corporate fascist must be stopped."

He added: "They say mercury in fish is dangerous but forcing all of our children to be injected with mercury in thimerosol is no risk. Make sense?"

He was referring thimerosal, an organomercury compound used as a preservative in vaccines also known as thiomersal.

The California governor's office did not immediately respond to requests for comment.

Brown's vaccine measure garnered support from both Republicans and Democrats after a measles outbreak in December in the Disneyland theme park affected some 130 people.

In total during the outbreak, 159 cases of measles were recorded between January and April in 18 states and the US capital.

The viral disease was believed to have disappeared years ago in the US thanks to vaccination programs.

But when some parents stopped vaccinating their children due to a range of beliefs, measles made a comeback.

The disease is highly contagious. It causes fever and rash and can lead to brain damage, loss of hearing or sight, and sometimes death.

Infants, the elderly and those with weakened immune systems are particularly vulnerable.