Cape Town, July 21 (DPA) A whale-watching expedition off the South African coast took a dramatic turn when a more than 10-metre-long whale crashed itself onto the deck of the yacht following it, the excursion members reported Wednesday.

Recounting the incident which they said occurred Sunday, the two amateur whale-watchers said they were unhurt when the whale crashed onto their yacht, the ‘Cape Argus’ and smashed its mast.

The huge mammal then slid back into the sea offshore from Cape Town and swam away, apparently unharmed.

They had been watching the whale from some distance for about half an hour when it went underwater and out of sight, Paloma Werner of the Cape Town Sailing Academy told reporters.

Then suddenly the animal weighing an estimated 40 tonnes shot up through the water’s surface and crashed onto the boat.

South African nature protection officials meanwhile have called for an investigation, the news broadcaster E-News reported.

There were suspicions that the two whale-watchers had gotten too close to the animal. The rules call for boats maintaining a distance of at least 300 metres.