The Met said it believed two people were injured in the attack and added it was awaiting updates on their conditions.

“The circumstances are being assessed; the incident has been declared as terrorist-related,” the Met said shortly after 3 p.m. local time (10 a.m. ET).

Police said it did not believe there were other suspects and added the scene has been fully contained.

Gabriel Vigo, a 24-year-old security officer at Heathrow who lives in the area, told CNN he heard a few shots. From the window of his flat, he saw three bodies on the floor.

“The road was quickly closed too and there was a body next to Boots with something that looked like a device strapped to him,” he told CNN. “It was square-shaped but it looked like it was taped to his shirt.”

Another eyewitness, Gulled Bulhan, a 19-year-old student from Streatham, told PA news agency that the man had a “machete and silver canisters on his chest.”

Bulhan told PA he saw the man “being chased by what I assume was an undercover police officer — as they were in civilian clothing.”

The London Ambulance Service said it was called to the scene shortly before 2 p.m.

“We are working closely with the other emergency services and are treating a number of patients at the scene,” a spokesperson for the service told CNN.

London Mayor Sadiq Khan said he was being briefed on the situation and was in touch with the Metropolitan Police and local representatives. “Terrorists seek to divide us and to destroy our way of life — here in London, we will never let them succeed,” Khan tweeted.

Prime Minister Boris Johnson thanked the emergency services responding to the incident in Streatham. “My thoughts are with the injured and all those affected,” the PM tweeted.

Videos shared on social media showed a number of ambulance and police cars at the scene.

Local resident Dan Smith, who was at the scene, told CNN he saw an ambulance helicopter landing on Tooting Common outside his flat. “On the High Road there was a huge police presence and a wave of ambulances/paramedics arriving. Armed police behind the cordon and everyone was told to remove back,” he told CNN in a message.

Streatham High Road is a busy shopping street. Police have told people to stay away from the area. It asked people to “use restraint in circulating pictures and videos” of the incident, including images of the officers involved.

The road remained closed even after police said the incident was contained.

The incident comes just two months after police shot and killed a man on London Bridge in central London after an attack that left two people dead and three others injured.

CNN’s Sarah Dean and Sharon Braithwaite contributed reporting.