A large grey-blue humpback whale spotted in River Thames near London

LONDON (Reuters) - A humpback whale measuring at least 5 metres (16 feet) has been spotted in the River Thames just east of London almost exactly a year since a beluga whale was first sighted in the British capital.

"We are 99.9999 percent sure it is a humpback whale - there have been multiple sightings," said a spokesman for the Port of London Authority, which oversees the river.

A beluga whale named as "Benny the Beluga" spent over three months in the River Thames last year.

"It is not Benny, it is not a beluga," the spokesman said.

Humpback whales, once prized by hunters for their blubber, can weigh up to 40 tons and span 60 feet (18 meters) in length.

Humpbacks migrate tens of thousands of miles a year between the rich feeding grounds of the Arctic and breeding grounds in tropical waters.

(Reporting by Guy Faulconbridge; editing by Michael Holden)