The husband of a marine biologist who died during a diving incident in the Maldives this week has said that “something must have happened down there” in the caves where the victims were swimming.

Five Italian divers died during an underwater cave expedition on Thursday, authorities said.

The group were exploring the caves at about 50-60m depth in Vaavu Atoll, which is about 64km (40 miles) from the capital Malé.

They were reported missing after failing to resurface.

Among the victims is 51-year-old Monica Montefalcone, a TV personality, marine biologist and professor of tropical marine ecology underwater science at the University of Genoa. Her daughter, Giorgia Sommacal, 22, also perished in the incident.

Monica’s husband and Giorgia’s father, Carlo Sommacal, expressed his devastation and said his wife is “among the best divers on earth” and would not have put anyone in the group in danger.

“She would never have put our daughter's life or that of others at risk... something must have happened down there,” he told La Repubblica on Friday.

“Maybe one of them had trouble, maybe the oxygen tanks, I have no idea.”

It has also emerged that a sixth victim was due to take the trip underwater but backed out at the last minute, although it is unclear why she decided to change her mind, according to La Repubblica.

According to authorities, the group were part of a larger diving excursion when they attempted to enter cave structures known for strong currents and complex underwater tunnels. There were thought to have been 20 people on board a yacht that set sail on the trip.

Rescue teams rushed to the scuba hotspot, near the island of Alimatha, and later recovered one body inside a submerged cave, while the remaining four are believed to still be inside the same cave system.

Maldives government spokesperson Mohamed Hussain Shareef said that the cave “is so deep that even divers with the best equipment do not try to approach.”

“There will be a separate investigation into how these divers went below the permitted depth, but our focus right now is on the search and rescue,” he said in the aftermath of the incident.

Maldivian coast guard and military units launched a “high-risk” search and recovery operation using specialist divers, boats and aerial support but rough weather conditions in the area, including strong winds and an official yellow alert, made operations more difficult than expected.

The victims were later identified as Monica and her daughter Giorgia Sommacal; researcher Muriel Oddenino; marine scientist Federico Gualtieri and dive operator Gianluca Benedetti.