Dozens of children, many younger than 15, were killed in a Saudi-led coalition airstrike that hit a school bus in northern Yemen on Thursday, according to the Houthi-controlled Health Ministry.

The children were on a field trip when their bus was struck at a market, the first stop of the day; 50 were killed and 77 injured, according to the ministry.

Most of the children were inside the bus when the airstrike hit, according to a local medic, Yahya al-Hadi.

The International Committee for the Red Cross said a hospital it supports in Saada had received 29 bodies of "mainly children" younger than 15, and 40 injured, including 30 children.

"The hospital is very busy. They've been receiving wounded and dead since the morning and it is nonstop," Red Cross head of communications and spokesperson Mirella Hodeib said.

"Putting children in harm's way is horrific and deplorable and making them pay such a price is unacceptable," she said.

Houthi media broadcast graphic footage appearing to show the bodies of children. CNN has not independently verified these images.

A video from Houthi-run Al-Masirah TV shows several boys who appear to have lost their limbs. Two or more wounded children are seen sharing a single hospital bed, and one child -- soaked in blood -- screams as he is being treated at a health center.

In another video, which appears to show the immediate aftermath of the strike, several children's bodies lie under a blown-up bus. Some boys are seen regaining consciousness, their faces bloodied and limbs charred. (CNN)