Thirty-four students at a primary school in southwest China's Sichuan province were being treated after possible poisoning by an unidentified gas at lunch Thursday, state media reported.

Xinhua News Agency said the students at the primary school in Ya'an city smelled a strange odor when they were having lunch. Soon, many suffered headaches, vomiting and chest pains, it said.

Nearly 200 students were sent to hospitals for checkups, and 34 were admitted for treatment.

Xinhua said the problems were not life-threatening.

It said the source of the gas was not known.