"We estimate over 100 people were killed," Franz Rauchenstein, head of delegation for the ICRC in Yemen, told AFP after he travelled to the city of Dhamar where the air strikes hit.

He said that at least 40 survivors were being treated for their injuries in hospitals in the city, which lies south of the capital Sanaa.

The Saudi-led military coalition said earlier that it launched air strikes against a Huthi military target that "stores drones and missiles".

However, the Huthi television channel Al-Masirah said that "dozens were killed and injured" in seven air strikes that hit a building the rebels used as a prison.

The ICRC has sent medical teams and hundreds of body bags to Dhamar, saying that it had visited detainees at the location before.

"As we speak, the teams are working relentlessly to find survivors under the rubble" and are "currently collecting bodies," Rauchenstein said, adding that the chances of finding anyone else alive in the heavy debris "are very low".