A convoy of six Sudanese army trucks delivered the migrants to Dongola after a journey of hundreds of kilometres following their rescue on the Sudanese-Libyan frontier by troops from both countries.
Sudanese officials announced the rescue Wednesday, saying traffickers had dumped their victims in the border region's scorching desert, where 10 died.
Troops initially found about 300 hungry and thirsty victims, but they later came across even more.
"The total number rescued is 600, first 309, and then they found another 300," Abdul Latif Abdullah, the Sudanese Armed Forces commander in Dongola, told AFP.
More From This Section
Most of the victims appeared to be Ethiopian or Eritrean, but there were some Sudanese as well.
An eight-year-old girl in the group was taken immediately to hospital, officials said, while the others first stopped at an immigration facility before they too were to receive medical checks.
According to the UN High Commissioner for Refugees (UNHCR), an average of 600 refugees from Eritrea make their way to neighbouring Sudan each month.
Most want to continue onwards, to Israel or Europe, rather than stay in impoverished Sudan.
"They would try to cross the Mediterranean Sea via Libya."
Economic migrants or refugees often rely on people smugglers.
The UNHCR did not have access to the northwest border region.
"Should the army relocate this population to areas accessible to UNHCR we would want to have access to the population to assess their status," said the agency's Sudan representative, Mohammed Adar.
"Should they be refugees, we would stand ready to provide support," in cooperation with local officials, Adar told AFP.