London - A suspected stowaway found dead on a London street is believed to have fallen from the undercarriage of an incoming flight to Heathrow Airport, police said on Tuesday.

The man, who police believe was African and aged between 20 and 30, was discovered on Portman Avenue in the suburb of Mortlake, just south of the River Thames in west London, at around 7.55am on Sunday.

The road is around 15km east of Heathrow and directly under the main flight path for incoming aircraft.

The man “was not a member of air crew or a passenger”, London's Metropolitan Police said in a statement.

A police spokesperson said that the theory that he might have been a stowaway who fell from a plane was “one line of inquiry”.

The statement added that officers from Twickenham CID were appealing for help in identifying the man, who was wearing jeans, a grey hooded shirt and white trainers when he was found.

“The death is currently being treated as unexplained,” the statement added.

“The post-mortem was held this afternoon but the result will not be in until tomorrow (Wednesday),” a Metropolitan Police spokesperson told reporters.

The discovery comes just over two weeks after another suspected stowaway was found dead on board a British Airways flight that landed at Heathrow from Cape Town.

The body of the unidentified man was found in the landing gear bay of a Boeing 747, British Airways said. - Sapa-AFP