A beluga whale, a protected species usually found in cold Arctic waters, has swum into France's Seine river and reached a lock some 70 kilometres (44 miles) from Paris, officials said Thursday.

The whale was first spotted Tuesday in the waterway that flows through the French capital to the English Channel, and follows the rare appearance of a killer whale in the Seine just over two months ago.

It is currently near Vernon, about halfway between Paris and the port city of Le Havre, with authorities in Normandy's Eure department urging people to keep their distance to avoid distressing the animal.

"In order to carry out the necessary observations... an operation to keep it in place at the lock will be carried out this afternoon," the regional authorities said.

They did not specify the size, but an adult beluga can reach up to four metres (13 feet) in length.

While they migrate away from the Arctic in the autumn to feed as ice forms, they rarely venture so far south.

"Studies of its health are underway to determine the best measures to take to ensure its chances of survival," the Eure authorities said late Wednesday.

In late May, a killer whale -- also known as an orca, but technically part of the dolphin family -- was found dead in the Seine between Le Havre and Rouen.

The animal found itself stranded in the river and was unable to make its way back to the ocean despite attempts by officials to guide it.

The Eure authorities said lone belugas do sometimes swim further south than usual, and are able to temporarily survive in fresh water.