Several people were injured in a stabbing attack in a park in the English town of Reading on Saturday, and British media said police were treating it as "terrorism-related."

The Press Association news agency and Sky News quoted security sources as saying terrorism was suspected in the early evening attack in the city's Forbury Gardens park. Police said several people were taken to hospitals but did not confirm reports of fatalities.

However, a source told the Telegraph three people were declared dead at the scene and two were transferred to the emergency department of Royal Berkshire Hospital, where they were receiving resuscitation.

Police said one person was arrested and was in custody.

Britain's interior minister said she was "deeply concerned," and Prime Minister Boris Johnson said his "thoughts are with all of those affected by the appalling incident in Reading".

The local Thames Valley Police force tweeted that officers were called to the city's Forbury Gardens around 7 p.m. It said that "a number of people sustained injuries and were taken to hospital" and one man was arrested at the scene.

The Royal Berkshire Hospital said it was treating two casualties from the incident.

Witnesses reported that police cars and helicopters descended on the park in Reading, a town of about 200,000 residents 64 kilometres west of London. Police blocked off several roads in the city centre, and photos showed two air ambulances nearby.

Jason Brock, the leader of Reading Council, tweeted: "Concerning reports from Reading town centre — please stay clear of the area as Police are dealing with a serious incident."

Home Secretary Priti Patel, Britain's interior minister, posted on Twitter: "Deeply concerned to hear reports of an incident in Reading. My thoughts are with everyone involved, including police and emergency responders at the scene."

The incident came hours after a Black Lives Matter protest took place at Forbury Gardens.

Nieema Hassan, one of the organizers of Saturday's protest, said demonstrators had left by the time the violence occurred. In a social media post, she said she was "praying for the people that are affected. I hope they're OK."