Hopes were fading Wednesday for free diving champion Natalia Molchanova three days after she went missing during a recreational dive in the Mediterranean near the Spanish island of Ibiza.

Spanish rescuers were still searching for the 53-year-old record-breaking Russian sportswoman and will continue to do so until Sunday, a spokesman for Spain's Guardia Civil police said.

"The search for Natalia has not officially ended but, to our great regret, the probability of success is low," the Russian Free Diving Federation said in a statement.

Molchanova failed to resurface after diving without fins to a depth of 30-40 metres (98-130 feet) off the coast of Formentera island, adjacent to Ibiza, on Sunday, the international diving federation AIDA and her family said in a joint statement.

She became separated from her colleagues and probably got caught in a strong underwater current, the statement added.

"The cause of Natalia's disappearance is unknown, but she was doing what she loved. Natalia has a passion for free diving that burned so deep inside of her that she dedicated her life to it," it said.

Spain's rescue service deployed a helicopter, boat and several divers to search for the Russian at a depth of up to 100 metres on Sunday.

Her family also hired an underwater robot to search for her, the Guardia spokesman said.

- 'World's greatest free diver' -

Molchanova, a mother of two, is the most decorated free diver in the world, with 41 world records and 23 world championship titles.

Free diving is a form of underwater diving, in which divers hold their breath instead of using a breathing apparatus such as a scuba tank.

Her record for a finless free dive is 71 metres, set in May in Egypt.

Molchanova's other feats include holding her breath for nine minutes and diving to a depth of 101 metres using a fin.

"The world lost its greatest free diver on Sunday," New Zealand free diver champion William Trubridge, who is friends with Molchanova's son Alexey, wrote on his Facebook page.

"My thoughts are split between the memory of such an indomitable, but gentle woman, and the deepest condolence for Alexey and the family she left behind," he added.

Molchanova, who was born in Ufa in Russia's autonomous republic of Bashkortostan on May 8, 1962, abandoned competitive swimming at the age of 20 to raise her two children, Alexey and Oksana.

She discovered free diving when she was 40 and quickly developed a passion for the extreme sport, which has claimed the lives of many of its proponents.

In 2002, French diver Audrey Mestre, 28, died while on a free dive off the coast of the Dominican Republic to 171 metres when her lift balloon failed to bring her back to the surface before she ran out of air.

In June 2014 leading yachtsman Laurent Bourgnon, who had French and Swiss citizenship, disappeared in French Polynesia after a going on a free dive.
Source: AFP