Minke whale calf stranded in London's Thames River

A young minke whale was lost far from home on Monday, trapped in the Thames River upstream of London landmarks after it escaped from rescuers overnight.

Crews had worked for hours before being able to free the whale from a perilous stranding on a lock near Richmond in south-west London.

But as the calf was being taken for further health checks on an inflatable pontoon, it slipped back into the water.

It remained trapped without food between locks at Richmond and Teddington.

Maritime authorities were trying to recapture the whale so they could relocate it to safer waters.

They said a whale had never been seen this far up the Thames before, 153 kilometres (95 miles) from the river's mouth.

The sheer distance makes the whale's route back to safety extremely difficult, they added.

The whale, which measures about four metres (13 feet) long, was first seen at the lock near Richmond late on Sunday.

The area is known for wide tidal swings that easily reach over 5.5 metres (18 feet) high.

Hundreds of people gathered along the banks of the Thames to watch the rescue operation as night fell.

Port staff were joined by firefighters, coast guard members and marine animal rescue divers.

Minke whales, which are more typically found in the northern Atlantic and Pacific Oceans, can grow to a size of nine metres (30 feet).