Some had been discharged by late afternoon.
"It looks like it is another case of gas poisoning, but it is being investigated now," Nang said.
The Afghan government, however, did not suggest who may have been responsible for the apparent attack.
"We were in our classroom when I smelt a bad smell. Our teacher walked outside the class to find out whether the smell is just in our classroom or everywhere at school," Farida, a 12-year-old schoolgirl being treated at the local hospital, said.
"When she found out that the smell is everywhere at school she informed the principal of the school and then took us out of the classroom."
Series of attacks
Al Jazeera's Hoda Abdel-Hamid, reporting from Kabul, said the incident is the latest in a series of attacks against schoolgirls.
|Schoolgirls have been treated for dizziness and nausea following suspected gas attack [AFP]
"This has happened a couple of times before, mainly in the northern province of Kunduz. At the time, it was also said, that these girls were poisoned and officials pointed the finger at the Taliban and rightly so," she said.
"However, there is still no hard conclusion on who is behind this attack and what kind of poisoning is taking place."
The Taliban banned education for girls during their Afghan rule from 1996-2001, but have condemned similar attacks in the past.
They have, however, set fire to dozens of schools, threatened teachers and even attacked schoolgirls in rural areas.
In one attack in Kandahar in 2008,around 15 girls and teachers were sprayed with acid by men on motorbikes.
In parts of southern and eastern Afghanistan, particularly in Taliban strongholds, schools for girls still remain closed.