A whale swims next to a boat in the Strait of Gibraltar. Image: Reuters / APRIL BOYES/INSTAGRAM @ APRIL_GE

In a bizarre accident reported in Sydney, a whale hit a boat, killing one man and leaving another with serious injuries.

The incident took place on early Saturday morning when the two men, aged 61 and 53, were out on a fishing trip off La Perouse, south-east of Sydney. They were found unconscious in Botany Bay in their vessel. They were rushed to the hospital, but one of them succumbed to his injuries.

"Attempts to revive him were unsuccessful and the 61-year-old was declared deceased," police said in a statement issued later. The second man is being treated at a hospital and is said to be in a stable condition.

"A second male, aged 53, was assisted by witnesses. He was transferred to Foreshore Road Boat Ramp and treated by New South Wales (NSW) ambulance paramedics, before being taken to hospital in a stable condition," added the police.

The authorities have described it as "an absolute freak accident" since these incidents are extremely rare.

The police have said that the whale hitting the boat must have caused it to tilt, which led to the unfortunate incident. Meanwhile, an investigation has been launched into the case.

New South Wales Maritime executive director Mark Hutchings has warned that people need to stay at least 100 metres away from adult whales and 300 metres from a calf if they are out in the waters.

"Whales aren't there to harm anyone, but those interactions can happen," Hutchings told the ABC.

The big picture:

Similar incidents have been reported in the past. Last year, five people died after a boat capsized following a possible collision with a whale in New Zealand.

Earlier this year, eight people aboard a vessel in the Pacific Ocean had to be rescued after their boat capsized after a collision with whales.

As seasonal migrations take place each year, pods with as many as 1,000 whales and dolphins move across Australia and New Zealand. Researchers say each pod follows a leader.

Ocean research has also shown that the navigation systems of naval vessels cause confusion for whales and dolphins as they use echolocation for their own navigation. They usually flee in such situations, which is thought to be a major cause of whale and dolphin strandings and such accidents.

One of the biggest threats to their existence is collisions with ships and entanglement in fishing nets and equipment. According to the National Oceanic and Atmospheric Administration (NOAA), there have been 101 large whale vessel collisions since 2013 in the US West Coast Region alone.