Free-diving world champion Natalia Molchanova is feared dead three days after she went missing during a recreational dive in the Mediterranean near the Spanish island of Ibiza.

A spokesman for Spain’s Guardia Civil police said rescuers are still searching for the 53-year-old record-breaking Russian and will continue to do so until Sunday.

• ‘Lion killer’: vandals attack hunter’s home
• Cinema shooting in USA
• Australia Post contractors charged

“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 off the coast of Formentera island, near Ibiza, on Sunday.

It was a modest dive for Molchanova as her record depth without the use of fins is 71 metres, set in May in Egypt.

But a joint statement from the international free diving association and Molchanova’s family said she became separated from her three colleagues and probably got caught in a strong underwater current.

“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,” the statement read.

“She was an inspiration to all free divers and despite being one of the fiercest competitors in the world, she was always calm and relaxed during competitions.”

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

Her family also hired an underwater robot capable of searching a radius of nearly 500 metres to search for her.

“We are overwhelmed and in tears here, it is difficult to find words. Why has this happened? She was such a positive and benevolent person,” Andy Tutrin of the Zurich-based free diving federation AIDA said.

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.