About 300 students have been under treatment or observation in hospitals after they had a lunch in a primary school in southwest China's Sichuan Province, local sources said on Monday.

The students developed symptoms of headache, fever, vomiting, stomache and laxness since Saturday after they had a lunch in the Chongzhou City Experimental Primary School on Friday, the first day of the new term for them.

No deaths have been reported, confirmed local authorities.

"There were a few pupils in serious condition and they have been out of danger now," said Shen Ji, director of the provincial health department.

Some pupils have been discharged from hospital after treatment.

An expert team from Chengdu, the provincial capital, arrived in Chongzhou on Sunday to help with the treatment of the pupils.

Health experts said the poisoning was suspected to be caused by food, but the cause needed to be further investigated.

About 800 pupils had their lunch in the school on Friday.

There were still sporadic pupils who came to hospitals for treatment.

"All the treatment costs will be paid by the city government," said Chen Gang, vice mayor of Chongzhou.

The school has on Monday stopped all classes and will resume classes depending on the pupils' recovery, according to Chen.