LONDON (AFP) - A man was stabbed late Tuesday as violence erupted between several hundred football fans outside West Ham's stadium in London during a match against local rivals Millwall. Fans clashed outside Upton Park, throwing bottles and bricks and starting small fires as police moved in to try and stop the violence, witnesses and police said. Inside the stadium, fans later invaded the pitch when the final whistle blew as police and stewards battled to remove them. Play was also stopped during the match as small sections of the crowd burst on to the ground. Several hundred riot police, backed by mounted officers, lined the streets outside the stadium and a helicopter flew overhead in case of further possible violence as thousands of supporters left the stadium at full time. Some West Ham fans reportedly clashed with police as they left late Tuesday. "There were lots of scuffles and fights before the game. I saw a couple of people with bloody faces. There was lots of shouting and a lot of bottles were thrown," said John Whittingham, who lives near the ground. "People were throwing bricks but I haven't got a clue where they were finding them. Some people were trying to rip bollards off the pavement. There were also some small fires lit. Police said two people were arrested over the violence, which appeared to be planned. "It looks like there has been some planned trouble from fans," a Metropolitan Police spokesman said. A 44-year-old man was in a stable condition in hospital after being stabbed in the chest close to the stadium, police said. A kebab shop owner said the violence had continued after the match started, and had forced him to close his business near the stadium. "There were West Ham fans on one side and Millwall on the other. They were being kept apart by the police. There were West Ham fans for as far as you could see along the street," he said. "People were chipping bricks off buildings and throwing them at police. I saw one officer getting kicked as he was on the ground," a man, 19, said. Another witness suggested the violence was inevitable. "The thing is, between these two sets of fans, it's hatred," he said.West Ham won the League Cup second round match 3-1 after extra time. Millwall, who despite the best efforts of successive club officials to kick-out trouble makers, have long been infamous for the violent conduct of some of their fans.