Shocked tourists looked on as a major fight broke out in front of them at one of the UK's best known tourist spots.
The brawl erupted in Trafalgar Square in central London at around 4pm on Thursday.
Three men were stabbed during the battle and are being treated in hospital.
Police are linking the stabbings and say those involved were believed to be from eastern Europe.
Police are questioning 19 men who have been arrested.