The accusation by Doctors Without Borders comes after the military coalition denied any knowledge of the attack in the Huthi-held northern Yemeni city of Saada, while acknowledging a raid elsewhere.

"There is no way to deny that this is an air strike, everyone in Saada City heard it," an unnamed member of the agency, known by its French initials MSF, was quoted as saying in a statement late on Saturday.

"I live one kilometre (half a mile) from the prison and my house was shaking from the explosions."

The attack overnight on Friday created horrific scenes, with bombed-out buildings littered with bodies and hospitals overwhelmed.

Rescuers continue to claw through the rubble searching for survivors, MSF said.

The Iran-backed Huthis' health ministry said 82 people were killed and 266 wounded, the agency said. There was no independent confirmation of the figures.

The Saudi-led coalition -- which is backed by arms sales by countries including the United States, Britain and France -- has dismissed claims it was responsible as "baseless and unfounded".

But it did report strikes a few hours earlier on the Red Sea port city of Hodeida that knocked out Yemen's internet, complicating rescue efforts and compounding problems for the impoverished country.

- 'Terrible effects' -

"This is the latest in a long line of unjustifiable air strikes carried out by the Saudi-led coalition on places like schools, hospitals, markets, wedding parties and prisons," said Ahmed Mahat, MSF head of mission in Yemen.

"Since the beginning of the war we have frequently witnessed the terrible effects of indiscriminate coalition bombing on Yemen, including when our own hospitals have been attacked."

MSF said its staff had confirmed the prison in Saada, the rebels' northern home base, was destroyed, and that a nearby hospital had run out of beds to treat the wounded.

"The hospital is facing a very difficult situation... with casualties lying on the floor," a staff member was quoted as saying.

The attacks marked a rapid escalation of hostilities after a drone and missile strike on the United Arab Emirates -- which is part of the coalition -- killed three in the capital Abu Dhabi last Monday.

Yemen's civil war began in 2014 when the Huthis seized the capital Sanaa, prompting the Saudi-led coalition to intervene to prop up the government the following year.

Rights groups have long criticised the coalition for civilian casualties in its aerial bombardment.

According to the Yemen Data Project, an independent tracker, there have been almost 9,000 civilian casualties from coalition air raids since 2015.

The conflict has killed hundreds of thousands of people directly or indirectly and left millions on the brink of famine, according the UN which calls it the world's worst humanitarian catastrophe.