Story highlights Bus was speeding in heavy fog, investigation reveals

Authorities say 30 of the junior high school students were injured

New Delhi (CNN) At least 15 children died and 30 were injured when a school bus collided with a truck Thursday in northern India, authorities said.

"Some children are in critical condition, so casualties could rise," said Parashuram Singh, the deputy superintendent of police in the state of Uttar Pradesh's Etah district. He told CNN that the school bus was carrying around 60 junior high school students.

An initial investigation indicates the truck was speeding in dense fog, which likely caused the accident, the deputy said.

Etah district administration had ordered all schools in the district to remain closed until January 20 due to cold weather, Satish Pal, Additional District Magistrate (ADM) of the district told CNN. He said his department was making inquiries as to why this particular school remained open.

Anguished by the tragic accident in UP's Etah district. I share the pain of the bereaved families & condole passing away of young children. — Narendra Modi (@narendramodi) January 19, 2017

In a tweet, Prime Minister Narendra Modi said "anguished by the tragic accident in UP's Etah district. I share the pain of the bereaved families & condole passing away of young children. I pray that those injured in the accident in Etah recover at the earliest."

At least 15 children were killed and dozens more injured when their school bus collided with a truck.

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