A man has collapsed and died in a Mayfair street, prompting a large 999 response as police feared he had been poisoned.
Mobile phone footage and photographs on social media show a number of police cars and ambulances on Albemarle Street in central London, near the Royal Institution.
A police cordon is in place.
The London Ambulance service said it was called to a cardiac arrest at 15:14 BST.
“Sadly, despite our efforts, a man died at the scene,” an ambulance spokesman added.
A spokesman from the Metropolitan Police said: “Due to concerns the victim may have been exposed to a poison, specialist officers attended but found no evidence that would indicate the victim had been poisoned.
“There are no other reports of people being taken ill.”
Local business workers told the BBC the man who died was the driver of a couple visiting one of the exclusive jewellery shops in the area.
Police and ambulance crews were seen putting a tented cover around a body in the street.