Spanish police said Thursday they had arrested two Cameroonian migrants accused of killing up to ten Nigerians by pushing them from a boat into stormy waters after a fight during an attempt to reach Spain.

The two men were part of a group of around 50 sub-Saharan migrants who departed from Nador (northern Morocco) on December 3 for Spain. They were on an inflatable boat without a motor and ran into rough weather, police said in a statement.

"The worsening weather conditions caused unease on the boat, but the fight broke out when a Nigerian pastor started praying out of fear that it would sink," the statement said.

"That is when the detainees blamed the bad weather on the Nigerians who were praying and used the boards that covered the bottom of the boat to assault and throw overboard the pastor and the other Nigerian passengers."

Police said the surviving passengers were not sure how many people exactly were pushed overboard during the fight because it was night and visibility was poor.

Spanish coast guard officials found the boat adrift off the coast of Almeria in southern Spain on December 5 with 29 people on board, including a three-year-old.

Police believe between seven and ten passengers were thrown overboard by the two Cameroonian migrants.

"The rest of the passengers who did not survive perished due to the rough conditions of these types of voyages," the police statement said.

Police said officials became suspicious after noticing that the survivors appeared afraid of the two Cameroonians after they were brought ashore.

During questioning three of the surviving passengers told police what had happened during the crossing.

Police also found 1,500 euros ($1,800) on one of the detained which the survivors had said the two Cameroonian men had stolen from the victims.

Despite the danger, thousands of migrants fleeing war and hardship try to cross the 15-kilometre (nine-mile) Strait of Gibraltar from Morocco to Spain on makeshift boats and inflatable dinghies each year.

Spain's maritime rescue services last year came to the aid of 3,500 migrants found on boats off the country's coast, a 55-percent increase from the previous year.

At least 3,419 migrants lost their lives between January 1 and December 10, 2014 trying cross the Mediterranean, according to the UN refugee agency making it the deadliest route for migrants in the world.