About 20 people were arrested after mass disorder broke out in a city centre following Newcastle United's win over arch rivals Sunderland.

Up to 300 people were involved in the trouble in Newcastle's Bigg Market at around 7.30pm yesterday and extra officers had to be drafted in, Northumbria Police said.

It followed hours of drinking since United's thrilling, if narrow, early afternoon 3-2 win at St James's Park against their fiercest rivals.

Deputy Chief Constable David Warcup said: ''We will be investigating this outbreak and looking into how and why it happened. ''However, it appears at this stage that alcohol was a factor and that this is the sort of behaviour which happens when a large number of people have been drinking over an extended period of time.

''Clearly, some people were intent on causing problems and we will be trying to identify them as part of our inquiries.''

The match itself, one of the best derby games in years, passed off peacefully, the force said.

Afterwards there were minor skirmishes between the two sets of fans who goaded each other, but they were separated by mounted police and dog handlers.