Hundreds of school kids have fallen sick after eating candy in several towns in the southern Philippines, officials say.

About 1,350 elementary and high school students were treated in hospitals in nine towns overnight in the province of Surigao del Sur on Friday.

They complained of stomach cramps, diarrhea, vomiting and headaches, the province’s governor, Johnny Pimentel told AFP Saturday.

Most of the victims were discharged and only 250 still remain in hospital, Pimentel said. They are, however, expected to be discharged later in the day, he confirmed.

Police have arrested at least nine men and women who sold the sweets from a van while the children were on their lunch break.

Security forces are investigating whether the sweets were expired or were deliberately laced with poison, Pimentel added.

“The suspects had a plan to sell only to school children. They went around nine towns the whole day selling candies,” he said.

Pimentel added that police are still trying to establish why the group had traveled some 300 kilometers (190 miles) from their home province to sell the sweets.

The group, however, has denied that they meant to poison the children, reports said.

Police said the sweets were flavored with the popular tropical durian fruit.

The southeastern region of the Philippines is the country’s main producer of durian. The foul-smelling fruit is transformed into a myriad of food products including confectionery, ice cream and coffee.

Poor enforcement of food safety regulations has been blamed for past cases of food poisoning in the Philippines which has a population of 100 million people.