Survivors say 44 people have died of thirst after their truck broke down in the Sahara Desert in northern Niger, the Red Cross has told the BBC.
The six survivors, all women, walked to a remote village and are being looked after in Dirkou, Niger, Red Cross official Lawal Taher said.
They say several children are among the dead.
The Ghanaians and Nigerians were trying to get to Libya, reports Nigerien news site Sahelien.
So far no-one has visited the site to identify the bodies, Mr Taher added.
The route from Niger to Libya is one of the main ways migrants reach North Africa before crossing the Mediterranean Sea to get to Europe.
Crossing the Sahara is one of the most perilous parts of the journey as migrants are crammed into pickup trucks often with only enough room for a few litres of water, reports Reuters news agency.
Authorities told Reuters that is it almost impossible to know how many have died in the vast and unpoliced Sahara.
Last June, the bodies of 34 migrants, including 20 children, were found in the Sahara Desert near Niger's border with Algeria.
It appeared they had died of thirst after being abandoned by their smuggler, a government minister said at the time.