A beluga whale stranded in the Seine river in northern France for more than a week was removed from the water early on Wednesday in a risky rescue operation, but officials warned it was in poor health.

After nearly six hours of work by dozens of divers and rescuers, the 800kg cetacean was lifted from the river by a net and crane in the early hours and placed on a barge under the immediate care of a dozen veterinarians.

The beluga, a protected species usually found in cold Arctic waters, was then given a health check and driven in a refrigerated truck toward the coastal town of Ouistreham.

Upon arrival, the beluga will be installed in a seawater lock where it will be held for observation for several days before being released into the open sea.

But officials in Eure, where the beluga was stranded, said the whale was worryingly thin.

"It bodes, according to veterinarians, for a poor vital prognosis," the Eure prefecture said in a statement after the rescue operation, which it said was "particularly complex".

The four-metre whale was spotted more than a week ago heading towards Paris and was stranded about 130km inland from the Channel at Saint-Pierre-la-Garenne in Normandy.

Since Friday, the animal's movement inland had been blocked by a lock at Saint-Pierre-la-Garenne, 70km northwest of Paris, and its health deteriorated after it refused to eat.

The animal's rescue was hailed online after a nail-biting few days.

"Today is a great day for this beluga whale and for everyone involved in its rescue," conservation group Sea Shepherd said on its website.

But the operation to return it to the sea is not without risk, said Isabelle Brasseur of the Marineland sea animal park in southern France, part of a Marineland team sent to assist with the rescue.

"It could be that he dies now, during the handling, during the journey or at point B," in Ouistreham, she said.

Interest in the beluga's fate has spread far beyond France, generating a large influx of financial donations and other aid from conservation groups as well as individuals, officials said.

While belugas migrate south in the autumn to feed as ice forms in their native Arctic waters, they rarely venture so far. (AFP)