One man died and another was in hospital on Saturday in Australia after a whale struck and flipped their boat during a fishing expedition, authorities said.

Police said one man was pulled unconscious from Botany Bay, off the coast of Sydney, and later died, while the other was taken to hospital in a stable condition, police said.

"A whale has been involved, whoever would have thought that that would have occurred, it's terribly tragic," said New South Wales Police Minister Yasmin Catley.

State Emergency Services Minister Jihad Dib said it was "an absolute freak accident".

The boat "was likely to have struck or been impacted by a whale breaching, causing the boat to tilt, ejecting both men", police said in a statement. It did not identify the whale's species.

Australia's extensive coastline hosts 10 large and 20 smaller species of whales. While human deaths caused by whales in the region are rare, Australia and neighbouring New Zealand are hot spots for mass whale strandings on beaches.

Eight Danes were rescued in June when their sailboat capsized in the Pacific Ocean after a collision with one or two whales.