Stanley, Hong Kong
The massive fish kill covered a big swath of St. Stephen's Bay in a silvery hue, Apple Daily reported Monday.
Most were sardines, thousands of which were spotted struggling in the water.
A man, surnamed Chui, described the scene as "breathtaking", with the water covered in a film of silver from dead or dying fish for about 30 minutes on Sunday.
He said he tried to push some of the fish back out to the water but there were just too many of them.
Most had died, he said.
For a moment, Chui said he thought it was a sign of an impending natural disaster.
Scuba divers reported more dead fish further offshore.
Experts said they might have been disturbed by severe noise caused by passing vessels or by extremely hot weather.
Chong Dee-hwa, chairman of the Ichthyological Society of Hong Kong, said the Stanley incident could have been due to noise from large vessels.