A truck loaded with sand collided with a school bus early Thursday, killing at least 24 young children in the northern Indian state of Uttar Pradesh, police said.

At least two dozen other children were injured in the collision when the speeding truck collided head-on with the bus, said Javeed Ahmed, the state's top police official.

The children, between the ages of 3 and 12, were studying at a school in the town of Etah.

The state's education authorities had closed all schools in the district due to a severe cold wave, and Ahmed said authorities would check why the school had stayed open.

It is not yet clear what had caused the vehicles to crash, although collisions are a common occurrence on winter mornings, when northern India is frequently blanketed with thick fog.

Road accidents killed nearly 150,000 people in India last year, around 400 a day, according to the data from ministry of road transport and highways.

Prime Minister Narendra Modi tweeted his condolences to the victims' families.

"Anguished by the tragic accident in UP's Etah district," he said. "I pray for those injured in the accident in Etah recover at the earliest."