Photo: The Canadian Press

A team of explorers say they have discovered the world's deepest underwater cave, 404 metres (1,325 feet) down, near the eastern Czech town of Hranice.

Polish explorer Krzysztof Starnawski, who led the team, told The Associated Press Friday he felt like a "Columbus of the 21th century" to have made the discovery.

Starnawski, 48, found the cave Tuesday in the flooded limestone Hranicka Propast, or Hranice Abyss, which he has explored since 1998. He scuba dived to a narrow slot at 200 metres' depth and let through a remotely operated underwater robot, or ROV, that went to the depth of 404 metres.

In 2015, Starnawski himself passed through the slot and went to 265 metres' depth, realizing that was still far from the bottom and that the cavity was widening. After diving that far down, Starnawski spend must spend four or five hours in a decompression chamber. To explore the cave further, he needed a robot.

Speaking on the phone from his home in Krakow, southern Poland, Starnawski said Tuesday's discovery makes Hranice Abyss the world's deepest known underwater cave, beating the previous record-holder, a flooded sinkhole in Italy called Pozzo del Merro, by 12 metres (39 feet.)

The Czech Speleological Society said it thinks the cave is even deeper and will yield additional records.