The bus was hit by the Saudi fighter jets at a market in Zahyn, a town in Yemen’s northwestern province of Sa’adah, al-Masirah TV reported.
According to the International Committee of the Red Cross (ICRC), the bus was carrying children.
Johannes Bruwer, head of an ICRC delegation in Yemen, said in a tweet that most of the victims were under the age of 10.
ICRC said one of the hospitals it supports in the city of Sa'adah has "received dozens of dead and wounded" from the attack.
The ICRC warned that "under international humanitarian law, civilians must be protected during conflict."
People of Yemen have been under massive attacks by the Saudi-led coalition for more than three years. Since March 2015, Saudi Arabia and some of its Arab allies have been launching deadly airstrikes against Yemen’s Houthi Ansarullah movement in an attempt to restore power to fugitive former president Abd Rabbuh Mansour Hadi, a close ally of Riyadh.
The aggression has killed over 16,000 people and taken a heavy toll on the country's facilities and infrastructure, destroying many hospitals, schools, and factories. The offensive has, however, achieved none of its goals.