Detectives are not treating the incident as terrorism.
Police are working to confirm the identity of the man who was killed and inform his family.
Siraj, 46, who lives locally and did not wish to give his surname, was walking through East Street Market when he saw police cars and ambulances going past.
He followed them and found two injured people lying on the ground in the market.
“It was terrifying,” he said, adding that the area had “always been safe”, but now he feels “unsafe to send my kids to school”.
Cdr Stevens urged anyone who witnessed the incident to contact the police.