Red Crescent rescues hundreds of migrants from Tunisia desert
However, smaller groups of people remain stranded near the frontiers with Algeria and Libya.
Hundreds of migrants from sub-Saharan countries fled or were forced out of Sfax after racial tensions flared following the July 3 killing of a Tunisian man in an altercation between locals and migrants.
Sfax is a North African departure point for many migrants from impoverished and violence-torn countries hoping to find a better life in Europe.
Many of those expelled from Sfax were left to fend for themselves in harsh desert conditions near Tunisia's borders.
Abdellatif Chabou, president of the Tunisian Red Crescent, told AFP the charity had been authorised to pick up hundreds of migrants left without water or food in the militarised zone of Ras Jedir, on the Libyan border.
He said the organisation had provided shelter to "630 in total" between Sunday and Monday -- a figure which could increase in the coming days.
An AFP correspondent on Wednesday saw migrants, including a large number of children, in a makeshift shelter at a high school in Ben Guerdane, 40 kilometres (25 miles) west of Ras Jedir.
Two other groups have been taken to Medenine and Tataouine, further south.
Chabou said the migrants now in Ras Jedir "came from several places, a group from Tunisia and another from Libya".
He said the Red Crescent was feeding them and had brought 400 mattresses from Tunis to equip the schools where they are now being sheltered.
The situation is different just south of Ras Jedir, however.
Other migrants sent a video distress call to Human Rights Watch (HRW) on Wednesday, which it transmitted to AFP.
Bodies found in desert
"We are suffering. There are children, pregnant women. We're suffering here. We have not eaten anything since yesterday. We're going to die if we don't get help. Help us!" pleads one.
HRW said there are at least 100 migrants without food, water or shelter, and that some have been stuck there for several days.
NGOs are also concerned about the fate of dozens of other migrants, estimated by HRW to number between 150 and 200, scattered along Tunisia's western border with Algeria.
On Tuesday, a judiciary spokesman told AFP that the bodies of two sub-Saharans had been found in the Hazoua desert near Algeria.
Youssouf Bilayer, 25, from Ivory Coast, told AFP he had been arrested on July 4 in Sfax where he had worked for four years as a welder and was taken to the Gafsa area near the boundary with Algeria.
"We are suffering a lot. We were able to find a little water in the forest, but we've got nothing to eat. The police won't let people give us food, all we can do is charge our phones a little," Bilayer said.
The Red Crescent said the migrants who had been picked up were being sheltered in Medenine, Tataouine and Ben Guerdane to "allow time to prepare other smaller centres so our volunteers can provide better support" along with other international groups.
Chabou said the idea was to carry out "profiling" with the International Organization of Migration help to find out if "some are asylum seekers or if they want to return to their home country within the framework of the United Nations voluntary return programme".
He said that just 200 migrants from those picked up near the border with Libya said they wanted to go home. Most of the others asked to be taken to Europe.