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.
The harsh Sahara: By Martin Patience, BBC News, Nigeria
The unforgiving conditions of the Sahara Desert mean that a broken down vehicle is often a death sentence for migrants.
Niger serves as a transit point for West Africans hoping to reach Europe to start a better life.
Every year, tens of thousands of migrants cross the Sahara to reach Libya. From the Libyan coast they board rickety boats to ferry them to Europe.
Many drown in the Mediterranean but, perhaps, less well known, are the dangers they face while crossing the Sahara.
It's not known how many deaths there are every year - as it's a vast, ungoverned region. But many migrants die of thirst, while others are robbed and attacked by criminal gangs and security forces.
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.