More than 40 West African migrants died in the Sahara desert this week after their truck broke down in arid northern Niger, the Red Cross told Reuters on Wednesday.

Six survivors walked to a remote village where they said that 44 people, mostly from Ghana and Nigeria and including three babies and two other children, died of thirst, said Lawal Taher, the department head for the Red Cross in the Bilma region.

Reuters and the authorities in Niger were unable to immediately confirm their account, but Taher said the Red Cross had told officials and that a search for the bodies was underway.

The number of migrants who cross the Sahara has increased in recent years as impoverished West Africans risk their lives to try to reach Europe.

In one of the most perilous parts of the journey, thousands of migrants each week are crammed into pickup trucks for the days-long ride from Niger into Libya, often with only enough room for a few litres of water.

Authorities and aid organisations are able to keep track of the thousands of migrant deaths in the Mediterranean Sea between Africa and Europe, but is it almost impossible to know how many have died in the vast and unpoliced Sahara.

Last year, a report by 4mi, an affiliate of the Danish Refugee Council, reported that it is likely that more migrants die in the desert than at sea, according to testimony from migrants.