Marine scientists will have to euthanise about 34 whales that have stranded themselves on Kommetjie beach in the Western Cape on Saturday.

Nan Rice, head of the Dolphin Action and Protection group said a decision had been made to put down the part of a group of 55 false killer whales that could not be moved back into the sea.

About 20 of the whales had been rescued successfully.

"That decision has been made. I believe they may be doing it right now," she said.

Officials and volunteers had been struggling throughout the day to help the whales back into the sea.

"We have tried everything, but they just make a U-turn and keep rebeaching themselves," said Wally Peterson project manager for the Kommetjie Environmental Awareness group.

Rice said the whales would be shot through the head with a pistol.

"I feel quite sad, but it is the right thing to do," she said.

Rice said mass strandings are extremely stressful for whales and to save stranding whales is usually an extremely difficult task.

"They are huge animals and are stranded over a vast area. Unfortunately they (the volunteers) couldn't do it."

Rice said the whales, which weighs between 4600 and 5500 kg and grow to be between 4.6 m and 5.5 m long, probably stranded because of a "navigational error".

The NSRI earlier appealed to members of the public who want to help put the 55 beached whales back at sea, to rather stay away.

"The roads to the beach are blocked because of all the public support," said Lambinon.

"The best help people could be at the moment is to stay away."

Lambinon said six front-end loaders from the City of Cape Town helped put some of the whales back into the water.

The whales started beaching themselves at around 7.30am on Saturday.