At 11 p.m. on Tuesday, 29 of them were taken to Life General Hospital in the northern province and the rest to Son La General Hospital.
According to the latter, some of the victims were in stable condition by Wednesday afternoon, but the rest were still having symptoms like vomiting and headache.
On Tuesday night around 100 athletes, all aged 10 to 15, had dinner at the training center cafeteria. Soon afterward some of them began to vomit and complain of stomachache, dizziness and headache.
The patients had eaten chicken onion salad, winter melon soup, ribs, and fried eggs.
The Son La Department of Health said it has taken samples of the food and the test results would come in a day or two.