Daesh terrorist group claimed responsibility for Saturday night's attack in London which killed seven people and wounded dozens, the militant group's agency Amaq said on Sunday.

"A detachment of fighters executed yesterday's London attack," a statement posted on Amaq's media page said.

Police specialists collected evidence in the heart of London after a series of attacks described as terrorism killed seven people and injured more than 48 others. Prime Minister Theresa May called an emergency security cabinet session to deal with the crisis.

The assault began that night when a van veered off the road and barreled into pedestrians on London Bridge. Three men fled the van with large knives and attacked people at bars and restaurants in nearby Borough Market, police and witnesses said.

More than 48 victims were treated at London hospitals and a number of others suffered less serious injuries. Some of the 48 people injured are in a "critical" condition, London Mayor Sadiq Khan told reporters Sunday in comments broadcast by the BBC.