Locals said at least 100 were stranded on Thursday afternoon on a stretch between the Bossaso port and Mareero beach in the northern Puntland region.

"The ministry of environment and the fisheries ministry are collaborating to urgently investigate this extraordinary incident," the region's government said, promising a formal report into what may have caused the rare event.

The exact number of stranded mammals could not be confirmed, Puntland's environment ministry said, but added that "residents in the area estimated around 100 dolphins washed ashore."

The ministry also commended residents who managed to rescue 30 dolphins by getting them back into the water alive.

Witness Abullahi Muse said 140 dolphins had come ashore "and most of them are dead, even though some are still alive".

"This is a horrible incident," he added.

"We have never seen such an incident before."

Several other witnesses gave similar tolls.

The Puntland environment ministry said dolphins were sometimes beached due to illegal fishing nets or water contamination.

While this many dolphins being stranded has not been reported before in Somalia, distressed cetaceans have been washing ashore around the world.

Scientists and conservationists have expressed concern over the deaths, blaming indiscriminate fishing techniques.