A humpback whale has been washed up in a Sydney seaside swimming pool.

The 12-metre, 30 tonne whale was discovered by authorities, who said rough seas and a high tide washed the whale over a safety fence and into the public pool.

Shona Lorigan, from the Organisation for the Rescue and Research of Cetaceans in Australia had a word of warning for the public:

"It's very, very dangerous for everyone in the water. Because we don't know how it died, we don't know what kind of fluids, what kind of disease might be floating around with the animal.

"We really need to make sure that everybody stays clear, they don't go into the water and certainly not in this area at all."

The beach at Newport is closed because of the risk that the carcass might attract sharks.

Authorities hope the whale will float out of the pool area on the next high tide.