Riot police are trying to disperse hundreds of revellers at a suspected illegal rave in central London.
The Metropolitan Police said members of its Territorial Support Group were called in after bottles were thrown at other officers late on Saturday.
They had been trying to move people inside and outside a disused building in High Holborn. Seven arrests have been made for public order offences.
Hundreds of revellers are still inside the building, police said.
Police said elements of the crowd, estimated to number about 500 people, became aggressive after police asked them to move on.
A force spokesman said: “Most of the people are still there. They have gone back inside the building and are going ahead with the rave.
“Officers at the scene have a watching brief.”
Several police officers have sustained minor injuries in the incident.
Users of the blogging site Twitter have reported road closures in the area.
Police were first called to the scene at 2320 BST.
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