Four people were arrested after more than 600 gathered in Manchester for an anti-lockdown protest, police said.
The demonstration in Piccadilly Gardens was condemned by Greater Manchester Police (GMP) as “irresponsible” after the rules came into force on Thursday.
A number of police officers suffered minor injuries at Sunday’s event, which included one group of protesters travelling from Cumbria.
GMP are hunting for the organiser and have vowed to fine them £10,000.
The four arrested were held on suspicion of public order offences and 24 protesters were given £200 on-the-spot fines.
Assistant Chief Constable Mabs Hussain said: “I would like to use this opportunity to publicly condemn this gathering.”
He said that before and during the protest, officers tried to engage with the organisers and attendees to “explain the restrictions and encourage compliance”, but this was ignored.
“Whilst responding to this gathering, a number of officers were injured,” he said.
“This is unacceptable behaviour towards officers who were simply doing their job and protecting people.
“Investigators will now work to identify those responsible and ensure they face justice.”