By Achara Wisetsri
The students, who had difficulty breathing, felt light-headed, were nauseous and vomiting, were rushed to Nakhom Pattana Hospital.
Late on Friday, 16 of the students were being treated at the hospital and four had been sent home, hospital director Dr Komon Phuthawornsap, said.
The fire started at 10am in a 500-tonne pile of rubber and other material at the outdoor yard of the factory which sorted materials for recycling in Soi Nong Wa of tambon Map Kha.
Twenty fire engines tackled the flames which sent thick black smoke over Nikhomm Wittaya School, nearly five kilometres away.
The school director temporarily closed the school and sent pupils home after some 20 students became ill.