Protesters angry at the death of a black man following a police chase barricaded a road and threw bottles at officers amid rising tensions.
Wheelie bins, mattresses and debris blocked part of Kingsland Road in east London, where crowds gathered in response to the death of Rashan Charles.
Videos posted on social media show a line of officers walking back in retreat as items are launched towards them.
Scotland Yard said "a number of items including bottles" were thrown at officers attending a "planned protest" from 3.40pm on Friday, close to Middleton Road.
The police watchdog, the Independent Police Complaints Commission (IPCC), is investigating the events leading to the death of Mr Charles on Saturday.
Unverified footage on social media appeared to show at least one police officer attempting to restrain him on the floor of a shop at 1.45am, close to where the protest is being held.
The 20-year-old later died in hospital.
Police officers could no longer be seen at the site of the clashes but dozens of protesters, some masked, are still lining the streets.
Pedestrians, motorcyclists and cyclists are being told by the group not to travel through the barricade.
Scotland Yard said it is continuing to monitor the situation and several emergency vehicles are parked nearby.
Shattered glass litters the road, where a handful of protesters are holding Black Lives Matter placards.
The IPCC said in a statement on Friday: "We understand the concerns raised following Rashan's death.
"We will independently examine the circumstances of this incident, we will follow the evidence, we will consider whether there is an indication there may have been misconduct or criminality, and we will seek to answer the questions that Rashan's family and the community of Hackney understandably have."