The police, fire crews and the RNLI have worked through the night to try to free a whale stranded in the River Thames in south-west London.
The whale, believed to be a baby Minke, was spotted in Richmond Lock on Sunday evening - and has since been moved.
A vet will now assess whether it is strong enough to be released back to sea.
The BBC's Matt Graveling, at the scene earlier, said the future of the whale "still hangs in the balance".
It is thought the whale was first spotted earlier on Sunday a few miles up the river near Barnes Bridge, before becoming stuck on the lock's boat rollers in Richmond.
The Port of London Authority, which owns and operates the lock, said the whale had become stranded at about 19:00 BST.
RNLI rescuers arrived at about 21:00 to help the animal, which is approximately 3-4m long, off the concrete.
They were joined by fire crews and marine rescue divers, who tried for several hours to float the whale before it was successfully moved to a safer location.
Update on the #Richmond #Whale.— Matt Graveling (@mattgraveling) May 9, 2021
The RNLI have just left to applause from onlookers as they move the whale to a safer location.
The future of the whale still hangs in the balance. A vet will assess its health. pic.twitter.com/E1kjFcP8KB
Gareth Furby, at the scene, tweeted: "The rescuers need to be sure it will survive if taken back upriver. The whale has some injuries."
And Jake Manketo, 20, from Richmond, earlier said: "Everyone here is just hoping they get it out.
"We couldn't believe our eyes when we first saw the poor fella, not every day something like this happens in Richmond."
Minke whales are the smallest of the great whales, growing to about 10m and can usually be found throughout the northern Atlantic and Pacific Oceans.