Shoppers have been told to throw away food bought in three west London supermarkets on Wednesday evening, after a man was arrested on suspicion of injecting items using syringes.
A Sainsbury’s Local, Tesco Express and Little Waitrose on Fulham Palace Road, Fulham, remain closed as police investigate.
The affected items are thought to be processed meat and microwavable goods, Hammersmith and Fulham Council said.
The content of the syringes is unknown.
The man is being held on suspicion of contamination of goods with intention of causing public harm or anxiety.
The Metropolitan Police said officers were called at about 19:40 BST after a man was reported to be shouting abuse at people in the street.
The Met said: “It is currently unknown as to how many items have been contaminated, or what with. Investigations are ongoing to establish if other businesses in the area are involved in the incident.”
A Little Waitrose shopper, who lives on the same street as the stores, told the BBC: “It is a bit a worrying because I was buying milk at the time and the police were escorting everyone out.
“It was quite panicky because we didn’t know what was going on.”
In an “emergency alert” notice on social media, Hammersmith and Fulham Council said: “Members of the public are advised as a precaution to dispose of any food items bought from these supermarkets this evening.
“H&F Council’s Environmental Health team are now working with the supermarket branches affected.”