A man pushed a Just Stop Oil protester to the ground and launched another campaigner's phone into the air during a slow-walk protest in a road in London.
A video clip shows the man walking up behind the group in the middle of Mansell Street and grabbing banners from them.
Later he is spotted smacking a phone out of a campaigner's hand and shoves several other climate activists in the group of around a dozen people.
The Met Police said the incident happened before officers arrived.
The video clip shows the man pushing over protesters who were slow marching in London
Just Stop Oil also held another traffic-blocking protest nearby, from Queen Victoria Street to Fleet Street, in central London.
The group have been taking part in daily slow marches since April 24 which has sparked anger from drivers.
In a statement, the Metropolitan Police have urged the public not to intervene when protesters are blocking the road.
A spokesperson for the force said: "The Met and City of London Police are aware of an incident in which a member of the public appears to have remonstrated with Just Stop Oil protesters this morning, 19 May, in the City of London, before the arrival of police.
"At this stage, we are not aware that any allegations have been made in regard to this matter.
"We completely understand the frustration and anger of London's communities when protesters walk slowly in the roads.
"We urge people not to intervene and to wait for the arrival of police, who will attend the scene promptly."
Just Stop Oil is calling for an end to all new oil, gas and coal projects in the UK and says its protests will continue indefinitely.
The man was also seen smacking a protester's phone into the air
A spokesperson said: "We understand how frustrating it can be to be disrupted.
"However, as of this morning, 13 people are dead and 13,000 people have had to be evacuated from their homes in Italy, due to six months' worth of rain falling in a day and a half.
"The disruption we are seeing on British streets is nothing compared to the disruption wrought if we do not stop licensing new oil, gas and coal."