Anti-vaccination protesters clashed with police in London on Friday as some tried to storm the offices of the UK regulator that approves vaccines, with police saying four officers were hurt.
The latest protest, comprising dozens of demonstrators who massed at several sites through the afternoon, comes after anti-vaxxers previously targeted UK television broadcasters' offices.
A livestream of the demonstration showed protesters trying to push past a police cordon to enter the office of the MHRA (Medicines and Healthcare Products Regulatory Agency), which was the world's first regulator to approve a coronavirus vaccine for public rollout in December last year.
They later moved towards central London and gathered outside the Science Museum, where police appeared to clash with the demonstrators and make arrests.
"A number of protesters have become violent towards police. Four of our officers have been injured during clashes," the Metropolitan Police said, adding "this is unacceptable".
The force had earlier tweeted that it was attending a demonstration outside the MHRA offices on Cabot Square in east London and "guarding the entrance to the building".
Video posted on social media showed the protesters reaching the doors, with security guards on the other side.
Seconds later, police pushed their way through the crowd and formed a cordon outside the building's entrance and scuffled with protesters trying to get in.
The mask-free demonstrators shouted that they were there "to protect the next generation" as they rallied outside, a livestream showed.
The protest came as Britain continues its successful mass vaccination drive, which has seen more than three-quarters of adults received two doses of approved jabs.
An independent panel of experts on Friday recommended the government does not extend the program to vaccinating all UK children aged 12 to 15.