Several people had been stabbed in the southern English town of Reading, British media report.
Police say they are investigating reports of an incident.
Sky News said the stabbings took place at the site of a Black Lives Matter protest in the town earlier on Saturday.
Video footage posted on Twitter showed paramedics rushing to help at least three people who were bleeding on the ground in a park. The footage could not be verified independently.
The head of the local council authority Jason Brock said police were dealing with a "serious incident" and urged people to stay away from the town centre.
British Home Secretary Priti Patel said she was "deeply concerned" to hear the reports.
"My thoughts are with everyone involved, including police and emergency responders at the scene," she tweeted.