A group of masked men blocked roads leading to Britain's busiest ferry port on Saturday in what officials said appeared to be an anti-immigration protest.

The Port of Dover said all traffic in and out was "stopped due to an ongoing public order incident," and police said they were "engaging with the protesters." Video posted on social media showed several dozen men in black, their faces covered, standing across a major road near the port.

One clip showed demonstrators linking arms across a main road and shouting "stop the boats." Chris Vinson, a Conservative Party local councilor, said the protest appeared to be "illegal migration-related." "I'm not aware that there's been any violence, although clearly, having the path of your vehicle blocked by men wearing black paramilitary gear and balaclavas is extremely intimidating," he said.