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Geograph/Hugh Venables
More than 500 people are at a rave in a Norfolk forest on the weekend new lockdown measures over illegal gatherings came in to force.
Since Friday police in England have been able to fine organisers of illegal gatherings of more than 30 people, such as raves, up to £10,000.
Police said the unlicensed music event has been going on in Thetford forest since about 23:20 BST Saturday.
The force said the rave was "extremely disappointing to see".
After a member of the public reported seeing large numbers of cars queuing to access a fire route, police found the event near to the English Heritage site Grimes Graves.
Coronavirus 'a real threat'
Paramedics have also been called after reports a man had become unwell.
Assistant Chief Constable Nick Davison said it was "clear this is a well-established and planned event which is due to go on until tomorrow".
"Due to the number of people at the event, additional policing resources will be needed and this will take time to resource.
"Coronavirus is still with us and continues to be a real threat so it's extremely disappointing to see these types of events taking place when the rest of our communities are doing everything they can to help stop the spread of the virus."
West Yorkshire Police said eight people were fined £10,000 for parties in the Headingley and Burley areas of Leeds, including two DJs at a party, and also seized equipment.
The force said a 27-year-old man from Lincoln has been charged with causing a public nuisance after a gathering on Wepener Mount, Harehills, on Saturday.
Supt Chris Bowen said the force "hope people will recognise the ongoing risks of holding or taking part in events such as this".
Meanwhile, police in Harlow in Essex seized thousands of pounds worth of equipment ahead of an unlicensed music event on Saturday afternoon.
Essex Police urged those planning to go to such events to "think again".
Ch Insp Lewis Basford said the force would be "looking to identify the organiser and take them to court".
He added: "My final message is to the organisers: we will seize the equipment - I don't care if you've hired it from someone or if it's yours, we will break up your event, and we can now fine you up to £10,000."
West Midlands Police said it had dealt with about 90 reports of possible breaches of restrictions "but we've not had to use our enforcement powers".
Home Secretary Priti Patel has said the legislation represents a crackdown on "the most serious breaches of social distancing restrictions".
But Metropolitan Police Federation chairman Ken Marsh said the legislation will mean "absolutely nothing" for enforcement in London.
"People just set up a music box in the middle of the street and say 'it's not mine', it's utter nonsense," he said.