Police have issued more than £15,000 in fines after 300 people attended an illegal rave in a railway arch.
Officers raided an unlicensed music event in Nursery Road, Hackney, at 01.30 GMT on Sunday.
Many people fled the scene, while organisers padlocked the doors from the inside to stop officers getting in, police said.
No arrest were reported, but 78 fines of up to £200 for breaching lockdown restrictions were issued.
A dog unit and helicopter were deployed to the scene, with police saying they made numerous attempts to contact the organisers.
Ch Supt Roy Smith said: "This was a serious and blatant breach of the public health regulations and the law.
"Officers were forced, yet again, to put their own health at risk to deal with a large group of incredibly selfish people who were tightly packed together in a confined space - providing an ideal opportunity for this deadly virus to spread.
"Not just organisers, but all those present at such illegal parties can expect to be issued a fine."
There is an England-wide lockdown in place which prevents any social mixing between households.
Under these restrictions people are asked to only leave home for limited reasons such as shopping, going to work, seeking medical assistance or avoiding domestic abuse.
The Met Police has broken up several large gatherings in London over the last month including a 150-person wedding at a north London school.
Two officers were injured as police broke up a party involving about 200 people in Kensington on 17 January.
Officers raided an unlicensed music event in Nursery Road, Hackney, at 01.30 GMT on Sunday.
Many people fled the scene, while organisers padlocked the doors from the inside to stop officers getting in, police said.
No arrest were reported, but 78 fines of up to £200 for breaching lockdown restrictions were issued.
A dog unit and helicopter were deployed to the scene, with police saying they made numerous attempts to contact the organisers.
Ch Supt Roy Smith said: "This was a serious and blatant breach of the public health regulations and the law.
"Officers were forced, yet again, to put their own health at risk to deal with a large group of incredibly selfish people who were tightly packed together in a confined space - providing an ideal opportunity for this deadly virus to spread.
"Not just organisers, but all those present at such illegal parties can expect to be issued a fine."
There is an England-wide lockdown in place which prevents any social mixing between households.
Under these restrictions people are asked to only leave home for limited reasons such as shopping, going to work, seeking medical assistance or avoiding domestic abuse.
The Met Police has broken up several large gatherings in London over the last month including a 150-person wedding at a north London school.
Two officers were injured as police broke up a party involving about 200 people in Kensington on 17 January.
