Police are investigating the case of two stowaways on a flight from South Africa to London after one man was found in the wheelwell of the plane when it landed, and the other apparently fell to his death, landing on a London rooftop.

The two unidentified men reportedly climbed into the wheelwell of a British Airways Boeing 747 at an airport in Johannesburg and managed to survive the 11-hour, 8,000-mile flight to London before one of the men fell Thursday, Sky News reported

The men were likely exposed to temperatures as low as minus-76 degrees Fahrenheit.  

The body of a man found on the roof of a business in southwest London is believed to be the stowaway. British police say the victim fell as the plane came into land over Richmond, which is below the flight path to Heathrow Airport.

"At this time there is no evidence to link the death to the discovery of a stowaway in the undercarriage of a plane at Heathrow Airport; however this is one line of enquiry into identifying the deceased and the circumstances of his death," London police said in a statement.

A spokesman for the e-commerce retail company NotOnTheHighStreet.com said police and emergency workers found a body on the rooftop of its offices that was unexplained.

The spokesman  said the body was unrelated to the business or its team members and added the company was "co-operating with the ongoing police enquiry."

An autopsy on the victim is expected.  

The unidentified survivor—between 25 and 30 years old— was found by airport staff and is in serious condition in a London hospital.    

British Airways said it was investigating the circumstances of the case."We are working with the Metropolitan Police and the authorities in Johannesburg to establish the facts surrounding this very rare case," the airline said in a statement.

No arrests have been made.

There have been previous cases of stowaways falling from planes in the Heathrow flight path area in southwest London. In September 2012, Jose Matada died after falling from the undercarriage of a Heathrow-bound flight from Angola on to a road in Mortlake, about a mile from Richmond. Matada, 26, is believed to have survived temperatures of up to minus 76F for most of the 12-hour flight, investigators learned.

He was "dead or nearly dead" by the time he hit the ground.

In July 2013, a suspected stowaway from Turkey was found frozen to death in the undercarriage of a BA jet from Istanbul to Heathrow. He died after facing temperatures of minus 76F during the four-hour flight.