The beluga was spotted in the French waterway on Wednesday after straying thousands of miles away from its home in the Arctic.

A drone was used to monitor the whale as it swam through a stretch of the river between Paris and the city of Rouen in Normandy.

But the animal is said to have "barely moved" on Thursday and on Friday appeared to be swimming a 25-mile stretch between two sets of locks northwest of the capital.

The beluga snubbed a catch of herring offered by conservation group Sea Shepherd France on Friday - prompting concerns it is slowly starving to death.

They tweeted: "For the moment, the beluga is not interested in the fish offered to it. We remain hopeful that he agrees to feed."

In the early hours of Saturday morning an update said: "Our teams took turns with the beluga all night long. He always ignores the fish offered to him.

"We will take stock of the situation with the state services during the day."

An earlier tweet said: "Beluga in the Seine: we are with him currently, the animal is extremely thin. The absolute urgency is to try to feed it, which we are going to do today. The success of the operation will depend on his reaction."

The animal has not responded to attempts to guide it back to safer waters and has displayed a "fleeing behaviour vis-a-vis the boats," officials said.

Volunteers trying to help are being as unobtrusive as possible in a bid to "avoid stress that could aggravate its state of health", a statement said.

The beluga swam away from boats trying to guide it towards the river mouth, between the sea ports of Le Havre and Honfleur on Friday.

Removing it from the water could put it at risk, said the president of Sea Shepherd France, Lamya Essemlali.

But the whale is "condemned to die if it stays in the Seine", Ms Essemlali warned on Friday.

Beluga whales are recognisable for their pale skin and bulbous foreheads.

They are sociable animals which habitually live, hunt and migrate together in pods.