A stowaway has fallen to his death onto a London office block after clinging to a passenger plane that flew more than 12 000km from Johannesburg to the UK, reports said on Friday.

Another stowaway is believed to have survived the journey and is in a serious condition in hospital.

The man died as the British Airways Boeing 747 came in to land at round 09:30 on Thursday, reported Sky News. He apparently landed on the roof of NotOnTheHIghStreet.com.

British Airways said it was working with UK and South African police to establish what had happened.

The victim, who was aged between 25 and 30, was found lying on top of an electrical box with his legs in the air, reported UK tabloid The Sun.