Secret Service agents were forced to employ violence as at least four people rushed the stage at a Bernie Sanders rally.

The US presidential candidate was speaking at a rally in Oakland, California, when agents were forced to swarm around him.

The protesters - a mixture of male and female - were quickly detained, while one agent used a baton to apparent hit one of the intruders.

Video shows one of the agents wrapping his arms around Sanders in a bid to protect.

Shortly after the protesters are led away, the crowd starts cheering "Bernie" while the Democrat politician announces "we don't get easily intimidated".

It is unclear how many people were detained and why they were protesting.

Sanders, a US senator from Vermont, is running far behind Hillary Clinton in the race for the Democratic nomination for the November 8 presidential election