The incident in Ladbroke Grove was captured on video
Police were pelted with bottles during two stand-offs at the Notting Hill Carnival.
About 180 youths were stopped and seven arrested at south London's Oval cricket ground as officers stopped the group from going to the weekend event.
Later officers were hit with bottles when they clashed with 40 people in a separate incident in Ladbroke Grove.
A total of 330 people were held during carnival with weapons such as knives, a Taser gun and CS spray being seized.
One eyewitnesses described the Ladbroke Grove clash as a "full-scale battle".
One officer suffered facial injuries during the skirmish, police said.
History of disorder
In the first incident, on Monday afternoon, officers stopped a group of about 180 people in Harleyford Road, outside the Oval.
Police said 151 were taken to a police station, of which seven were formally arrested for public order offences or possession of pointed or bladed items.
Bottles were thrown at police in Ladbroke Grove
Officers said they believed the group, which included many teenagers, were on their way to the carnival to commit crime.
Some members of the group had a history of being involved in disorder at the carnival, police said.
Later in the evening police were involved in sporadic clashes in Ladbroke Grove, near the carnival route in west London, where unprotected officers were hit by bottles and other objects.
Up to 40 people were involved in the clash, which continued for more than two hours, and one officer suffered facial injuries after being hit by a bottle.
Ch Insp Jo Edwards said: "For over two hours our officers were faced with a hardcore, mainly of young men, who came to Carnival not to enjoy the event but to fight, commit crime and cause trouble."
Pat Mason, from Kensington and Chelsea Council, was at Ladbroke Grove and saw the events unfold.
I saw one police officer with blood on his face and I saw people who were throwing missiles getting carried away because they were getting batoned as well
Pat Mason, eyewitness
He said: "They were all picking up bottles, throwing bottles, throwing bits of stones, throwing anything at the police they possibly could.
"I saw one police police officer with blood on his face and I saw people who were throwing missiles getting carried away because they were getting batoned as well.
"So we had a full-scale battle going on."
Ch Insp Edwards said the majority of the 330 reported crimes during the two-day carnival, which attracted about 850,000 people, were as a result of stop and search powers.
Last year 246 people were arrested over the same period.
Carnival organisers said the trouble which flared after the event was "extremely disappointing".
But Michael Williams, from London Notting Hill Carnival Ltd, said: "More than a million people had a great time at the Notting Hill Carnival and enjoyed an amazing spectacle of colour, energy and music."
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