The whale was seen in the water in southwest London just hours after escaping crews who had freed it from a lock where it was stranded.
Rescuers have said they are worried about the young mammal’s health and feared it may be unwell.
They had freed the whale in the early hours of Monday and were taking it to a deeper part of the river in an inflatable cushion when it escaped.
Hundreds of people gathered at Richmond Lock and Weir in west London on Sunday evening after the three to four-metre long mammal was spotted, stranded on the lock’s boat rollers.
The whale was kept damp by staff from Port of London Authority (PLA) hosing it down. A vet performed a check-up on the river’s edge with the Royal National Lifeboat Institute (RNLI) after appearing at the scene to cheers from the crowd at around 9pm.
Footage posted from the scene showed the whale finally being freed at about 1am.
But hours after the rescue effort, the animal was spotted on the move in the water near Teddington Lock just after 10.20am, heading downstream towards Chiswick and then back towards Richmond Lock and Weir where it was previously stranded.
A RNLI spokesperson said Chiswick’s RNLI crew worked with the fire rescue service, police and British Divers Marine Life Rescue to try to free the whale on Sunday evening.
“Together they managed to free it and were taking it to a deeper part of the river when it swam away,” they said.
“The whale was displaying concerning behaviours and experts in attendance were concerned that it may be unwell.”
After the whale was finally freed at about 1am on Monday morning, it was moved to a more “stable” location, said the London Fire Brigade. It would be assessed to see the scale of its injuries and whether or not it can be released, reported the BBC.
Martin Garside, a spokesman for the the Port of London Authority, which operates Richmond Lock, said he thought it is the furthest a whale had ever been known to swim up the Thames.
“It’s 90 miles from the North Sea – that’s quite an achievement,” he said.
It is believed the whale was first spotted at Sunday lunchtime by filmmaker Gareth Fubry, a few miles up the river near to Barnes Bridge.
A spokesman for the PLA, which operated the lock said: “At around 7pm on Sunday, a small whale, approximately 3-4m long, believed to be a Minke whale, became stranded at Richmond Lock and Weir.
“PLA staff have attempted to assist the whale with water along with British Divers Marine Life Rescue.”
Martin Garside, a spokesman from Port of London Authority said that its release was only a “mild success”.
He explained: “It is a mild success in the sense that the animal is no longer trapped on concrete – but that whale’s life hangs in the balance: it is injured, it is very young and it is so far from home,” reported Reuters.
Minke whales are the smallest type of whale and typically grow to about 10m long.
They are usually found in the northern Atlantic and Pacific Oceans but can be found at the ice edge in the Arctic during the summer and south, near to the equator, during the winter.
In 2019 three whales were found dead in the Thames, including a minke and a humpback.
Additional reporting by Press Association