Only one survivor has been found since the Super Puma helicopter crashed during exercises last evening, an air force spokesman told AFP.
A large-scale search including naval, police and maritime rescue services was underway of the area, 25 nautical miles southwest of the archipelago's Fuerteventura island, the spokesman said.
"They were doing a regular rescue by winching exercise when it crashed," he said.
The cause of the accident was as yet unknown.