(CNN)At least four people at a Bernie Sanders rally in Oakland rushed the stage Monday evening, spurring Secret Service agents to jump onto the raised platform and protect him. The Democratic presidential candidate was uninjured and continued speaking, but not before several agents hugged him and pushed him away from the microphone. The identities of the individuals, who yelled as they approached the stage, were not immediately known. They were apprehended and led away by Secret Service from the podium at the Frank Ogawa Plaza, where the rally was being held. It's not the first time in the 2016 campaign season that Secret Service have jumped on stage when commotion broke out around a protectee. In March protestors stormed the stage at a Donald Trump rally in Dayton, Ohio, prompting Secret Service to react similarly by hopping on stage to shield the candidate. After the events of Monday night in Northern California, Sanders spokesman Michael Briggs said, "It was handled professionally by the Secret Service." The Vermont senator began receiving Secret Service protection in early February during the early part of the presidential primary season, in his challenge to Democratic front-runner Hillary Clinton.