Yemen's state news agency Saba, said the camp at Haradh was hit by Saudi planes.

It said the dead included women and children, and showed the bodies of five children laid out on a blood-streaked floor.

The International Organisation for Migration, which initially reported 45 deaths, said 40 people were killed and 200 wounded - dozens of them severely hurt.

The medical aid organisation Medecins Sans Frontieres said at least 34 wounded people were brought to a hospital in Haradh which it supports. Another 29 were dead on arrival.

"People in Al Mazraq camp have been living in very harsh conditions...and now they have suffered the consequences of an air strike on the camp," said Pablo Marco, MSF operational manager for Yemen.

Mazraq, in the province of Hajja next to the Saudi border, is a cluster of camps that are home to thousands of Yemenis displaced by over a decade as well as East African migrants.

In the capital Sanaa, controlled by the Houthis, jets struck around the presidential palace overnight and made more raids throughout the day.

Most of the air strikes, launched on Thursday, have taken place so far only at night.

In the south, Houthi fighters closed in on the port city of Aden, the last major stronghold of Hadi supporters, and residents said Egyptian warships shelled a column of Houthis advancing along the coastal road.

A Reuters reporter heard heavy explosions and saw a thick column of black smoke rising from the area about 15 km northeast of Aden and witnesses reported at least one plane flying nearby.