Bomberna släpptes över ett fängelse i staden Sadaa, i en provins med samma namn i nordvästra Jemen där Huthirebellerna har ett starkt fäste.
Bilder från nedslagsplatserna visar mängder av döda kroppar i rasmassor och byggnader som jämnats med marken. Det är ännu oklart exakt hur många som har dödats.
Dödstal väntas stiga
Ett sjukhus har tagit emot åtminstone 70 döda och ett hundratal skadade, enligt Läkare utan gränsers företrädare i landet. Flera andra sjukhus har tagit emot drabbade.
- It is impossible to know how many people have been killed.
It seems to have been a terrible act of violence, says the medical organization's Yemeni chief Ahmed Mahat.
- What I hear from my colleague in Saada is that there are still lots of bodies where the attack took place, with many missing.
The International Federation of Red Cross and Red Crescent Societies (ICRC) also counts the number of victims at least one hundred.
- The numbers will rise, says ICRC spokesman Basheer Omar.
According to Save the Children's international organization, migrants have been detained in the affected prison.
It counts the number of confirmed dead to at least 60.
Playing children killed
During the night until Friday, the west coast city of al-Hudaydah was also attacked from the air, with the result that the whole of Yemen lost contact with the internet.
The attack was directed at the Yemeni telecommunications monopoly, which is under the control of the Huthi rebels.
In this attack, three children were also killed, according to Save the Children.
"The children are said to have been playing on an adjacent football pitch when the robots crashed," the organization announces.
The news agency AP has been able to confirm the destruction at the telecommunications company by comparing satellite images.
The Saudi-led alliance was behind the attack.
Saudi Arabia's state news agency reports that it was carried out to "destroy the capabilities of the Huthi forces" in al-Hudaydah.