The authorities have confirmed an investigation has begun into events at the London Stadium on Wednesday night with both teams also facing punishment from the FA
The fixture, typically played in a fraught atmosphere between London rivals, was subject to heavy stewarding and policing.
But problems developed late in the game, as stewards battled to maintain segregation between the two sets of fans with Chelsea 2-0 down.
A Metropolitan Police statement read: “Although the vast majority of people left the stadium peacefully and were well behaved, there were a minority of people who attended the match that were clearly intent on being involved in confrontation and violence.
“Despite extensive work with both clubs and the London Stadium partners as well as a large and robust policing operation, there were unacceptable incidents inside and outside the stadium, before, during and after the game.
“We welcome the condemnation from partners and have already started a post-match investigation.
“We have already made seven arrests and will work tirelessly to identify people involved and bring them to justice.”
West Ham “unreservedly” condemned the actions of sections of supporters swiftly after the game.
Previous incidents at matches against Watford and Middlesbrough – along with poor performances on the pitch – have made for a difficult start to life at London Stadium for West Ham, having left Upton Park at the end of last season.
Both teams could be subject to punishment from the Football Association, who have launched a probe into the ugly scenes.
A statement read: “The FA is investigating crowd disturbances at last night’s EFL Cup match between West Ham United ad Chelsea. We are in dialogue with all relevant authorities.”