A group of divers exploring a shipwreck in the Baltic Sea have found bottles containing what is thought to be the oldest drinkable champagne in the world, made in the late 18th century.

"I picked up one champagne bottle just so we could find the age of the wreck, because we didn't find any name or any details that would have told us the name of the ship," diver Christian Ekstrom.

Mr Ekstrom and his Swedish diving colleagues opened the bottle and tasted the contents.

"It was fantastic... it had a very sweet taste, you could taste oak and it had a very strong tobacco smell. And there were very small bubbles," he said.

Experts said the shape of the bottle showed it was from the late 18th century and the bottle and its contents have been sent to champagne specialists in France to be analysed.

"We are 98 per cent sure that it is Veuve Clicquot champagne and that it was probably [made] between 1772 [the year the business was established] and 1785," Mr Ekstrom said, adding that the cargo vessel was probably sailing to St Petersburg, then the capital of Russia.

He said they had found the wine on their first dive and did not yet know how many bottles the wreck contained or what other cargo it carried.

The current title of the world's oldest champagne is held by Perrier-Jouet, which has two bottles from 1825.

Richard Juhlin, a Swedish champagne specialist, told the newspaper Alandstidningen he believed the champagne was Veuve Cliquot and said that if it was from the late 18th century, it could cost around 500,000 Swedish crowns ($78,500) a bottle.

Because the wreck lies off Aland, an autonomous part of Finland, the local authorities will decide what will be done with the wreck and the champagne.

- Reuters