A search is under way to find a group of migrants after a man in his 20s was stabbed to death on a French beach. French police launched an investigation after a body was found on Terminus Beach, in the popular seaside resort of Berck-sur-Mer on Thursday.Witnesses reported the victim had been attacked by other migrants on the sand dunes at dawn. It is feared that the suspected murderers fled across the Channel to the UK by small boat soon after. That same day, at 6am, a small boat set sail from the same beach carrying 165 migrants. The vessel was later escorted into Dover for its occupants to be processed. The National Crime Agency is liaising with French police following the incident. A spokesperson for the NCA told the Daily Mail: 'We are aware of an incident on Thursday, July 23 in which an individual died in French waters.'French partners are leading the investigation into the circumstances'. Pictured: Berck-sur-Mer beach in northern France where a man was killed on ThursdayIt emerged more than 500 small-boat migrants arrived in Burnham's first week, with sources claiming one 'mega dinghy' was 12m long and carried 165 people (stock image) While the number of arrivals so far this year – more than 13,000 – is over 40 per cent down on last year, experts believe crossings could go up againThe Home Office declined to comment on the incident. French authorities are trying to identify the victim, who had no documents on him. A French investigative source told the Sun: 'There was a fierce argument, and fighting. A young man was stabbed by at least one attacker. 'A knife was close to his dead body in the afternoon, many hours later. 'By this time it is believed those responsible got on a boat and escaped to England.' The incident happened along a 7.5-mile stretch of sand in the commune of Berck-sur-Mer, which sits within Calais. Police were reportedly already in the area attempting to prevent migrants from crossing the Channel. More than 500 migrants crossed the channel on Wednesday and Thursday alone during Andy Burnham's first week as prime minister.