A suspected stowaway was found dead on board a British Airways flight that landed at London's Heathrow Airport from Cape Townon Thursday, the airline said.

The body of an unidentified man was found in the landing gear bay of a Boeing 747, British Airways said, adding that it was investigating how the "very rare and sad event" had taken place.

"We are liaising with the South African authorities and Cape Town airport after a body was found in the landing gear bay of one of ouraircraft," it said in a statement.

"Our thoughts are with the individual's family."

London's Metropolitan Police said there was an ongoing investigation to discover the man's identity.

"He was not a passenger or a member of the air crew," a police spokesman told AFP. "His death is being treated as non-suspicious."

The Airports Company South Africa (ACSA) said a man had scaled the perimeter fence at Cape Town International at around 8:40 pm (1840 GMT) Wednesday.

"The airport immediately responded and as a security patrol officer attempted to apprehend the man he ran in the direction of a British Airways aircraft already in its holding pattern ready for takeoff," it said in a statement.

"For safety reasons the security officer could not approach the aircraft."

Searches of the airfield and runway failed to uncover the missing man.

"This morning reports from London's Heathrow airport confirmed that a stowaway was found on board a British Airways aircraft. The person was found dead," said ACSA, saying it viewed the matter in the "utmost serious light" with a full investigation to be done.

"Security concerns and unauthorised access to airports premises and aircraft are a very serious concern to us," he said.

No details on the stowaway's nationality or age were available.

[British Airways flight via Christopher Parypa / Shutterstock.com]