A doctor examines a student at the Krông Ana District Medical Centre. — VNA/VNS Photo Tuấn Anh

ĐẮK LẮK — Four people who gave balloons to more than 30 primary students have been detained by the Krông Ana District Police in the Central Highlands province of Đắk Lắk.

Officers arrested three men and one woman. Two are foreigners and two are Vietnamese.

The district police are working with the provincial Department of Foreign Affairs to conduct further investigations, said a leader of the district police on Friday.

The incident happened at about 1.30pm on Wednesday at Lý Tự Trọng Primary School in Buôn Trấp Town, Krông Ana District.

Four people came to the school and gave balloons to the students.

About half an hour later, 31 students began to show signs of dizziness, headache, abdominal pain, and nausea.

They were then taken to the school’s medical room and the case was reported to local authorities.

Among the 31 students, 17 were admitted to the district medical centre. The other 14 with lighter symptoms are being monitored at home.

The students said that there was a kind of white powder on the balloons. They started to have the symptoms when they blew the balloons.

The principal of the Lý Tự Trọng Primary School said that the white powder tested negative for drugs.

All of the students are in stable conditions. — VNS