An airstrike by the Saudi-led coalition hit a bus driving in a busy market in northern Yemen on Thursday, killing least 50 people including children and wounding 77, Yemen's Al Masirah TV said citing Health Ministry figures.

The Saudi-led coalition, meanwhile, said it targeted the Houthis, who had fired a missile at the kingdom's south on Wednesday, killing one person who was a Yemeni resident in the area.

Al Masirah TV aired dramatic images of wounded children, their clothes and schoolbags covered with blood as they lay on hospital stretchers.

The International Committee of the Red Cross said on Twitter that its team at an ICRC supported hospital in Saada received the bodies of 29 children, all under 15 years old. It also received 48 wounded people, including 30 children, it said.

The attack took place in the Dahyan market in Saada province, a Houthi stronghold. The province lies along the border with Saudi Arabia.

The bus was ferrying local civilians, including many children, according to Yemeni tribal leaders who spoke on condition of anonymity for fear of reprisals.

There was no breakdown in the casualties and it was not immediately clear how many of the victims were on the bus itself and how many were pedestrians in the immediate area around it. It was also unclear if there were other airstrikes in the area.

Col Turki al-Malki, a spokesman for the Saudi-led coalition, said the attack in Saada targeted the Houthis who had fired a missile at the kingdom's south, killing one person and wounding 11 others.

The coalition said Wednesday's projectile, fired toward the southwestern Saudi city of Jizan, was intercepted and destroyed but its fragments caused the casualties.

The statement, carried by the official Saudi Press Agency, also said the missile was launched “deliberately to target residential and populated areas.”

Al-Malki insisted Thursday's attack carried out in Saada is a “legitimate military action” and is “in accordance with international humanitarian law and customs.” He also accused the Houthis of recruiting children and using them in the battlefields to cover for their actions.

Saudi Arabia backs Yemen's internationally recognised government and has been at war with the Houthis since March 2015. The Houthis control much of northern Yemen, including the capital, Sanaa.

“Scores killed, even more injured, most under the age of ten,” the head of the ICRC in Yemen, Johannes Bruwer, said on his Twitter account, adding that the ICRC in Yemen is “sending additional supplies to hospitals to cope with the influx.”

Later on Thursday, airstrikes hit the Yemeni capital, Sanaa, and sounds of the blasts reverberated across the city's southern and western neighbourhoods. It was not immediately clear if there were any casualties in those strikes.

Yemen's stalemated, three-year war has killed over 10,000 people, badly damaged Yemen's infrastructure and crippled its health system. The coalition faces widespread international criticism for its airstrikes in Yemen that kill civilians.

Impoverished Yemen, on the southern tip of the Arabian Peninsula, is now in the world's worst humanitarian crisis, with more than 22.2 million people in need of assistance.

Last week, Yemeni medical officials said the coalition conducted airstrikes in the port city of Hodeida, killing at least 28 people and wounding 70. But the coalition denied carrying out any attacks in the city, saying it follows a “strict and transparent approach based on the rules international law.”

The fight for the port of Hodeida, a key lifeline for supplies and aid for Yemen's population on the brink of starvation, has become the latest battleground in the devastating war.