The world's deepest underwater cave has been discovered by a team of explorers in the Czech Republic, measuring at least 404 metres (1,325 feet) deep.

The flooded limestone sinkhole, known as the Hranicka Propast or Hranice Abyss, is located in the Hurka u Hranic nature reserve in the country's east.

Some of the world's other deep dives: Pozzo del Merro in Italy (392 metres)

Pozzo del Merro in Italy (392 metres) Zacaton in Mexico (339 metres)

Zacaton in Mexico (339 metres) Vrelo Cave in Macedonia (330 metres)

Vrelo Cave in Macedonia (330 metres) Boesmansgat in South Africa (270 metres)

Boesmansgat in South Africa (270 metres) Dean's Blue Hole in the Bahamas (202 metres)

It has been surveyed numerous times by Polish explorer Krzysztof Starnawski over the last 20 years, but Mr Starnawski had never, until now, been able to measure beyond a depth of 370 metres (1,214).

A diagram showing a cross-section of the the Hranicka Propast. ( Facebook: Krzysztof Starnawski )

This time, during the expedition carried out on September 27, the team employed the help of a remotely-operated underwater robot (ROV) to explore the deeper, narrower depths of the abyss.

But the robot was still unable to find the bottom as it reached the end of its cord at 404 metres, suggesting the cave may actually extend much further down.

It was, however, more than enough to beat the previous record holder, the Pozzo del Merro sinkhole in Italy, by 12 metres.

The expedition was funded in part by National Geographic.

In an interview published on their website, Mr Starnawski explained that he had to dive down 200 metres (656 feet) before deploying the robot.

"During this push, the most important part of the job was done by the robot," he said.

"I scuba dived down to 200 metres just before the ROV's deployment to put in the new line for the robot to follow.

"The goal was to give the ROV a good start from there to the deepest part of the cave.

"The results were astonishing," he added.

On Facebook, the Hranicka Propast expedition team celebrated the record.

"We made it! Hranicka Propast is the deepest underwater cave on the planet!" it said.