The victims were discovered on Sunday, just hours after a lone survivor had been pulled to safety. An NGO said the boat had set sail with 34 people on board. 29 people are reported to be still missing.
Spain’s Salvamento Maritimo coastguard said on Twitter that it had “recovered the bodies of four people” from a boat some 150 nautical miles southwest of Gran Canaria.
There was one survivor, the maritime rescue agency said.
They were then rescued by a merchant ship passing by the area.
They are being taken to the city of Las Palmas, the coastguard added.
They are expected to arrive around 6am on Monday.
The campaign group Caminando Fronteras that it was a “tragedy” to report that one person had been discovered surrounded by four corpses.
Helena Maleno Garzon, of the group, added that 138 people are known to have disappeared on the migrant route to the Canary Islands in recent weeks.
A number of people thought to have been on the boat remain unaccounted for.
Ms Maleno Garzon quoted the father of a number of people whose whereabouts remain unknown.
He told the organisation: “At least they know something.”
The man’s wife and two children travelled in a separate vessel, it is understood.
He said: “Please don’t forget them.”
Travelling to Europe via the Canary Islands has become one of the most dangerous routes for those attempting to reach the continent.
In September, UN data showed that more than one thousand people had died or been lost at sea when trying to reach Europe through the Spanish islands.
The figure for the first nine months of 2022 was nearly as high as the mortality rate for the entirety of 2021, according to Spanish daily El Pais.