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.
GMP are hunting for the organiser and have said there will be fines of £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.
Whilst responding to this gathering, a number of officers were injured.
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.”