Humanitarian aid workers and medical supplies have begun to arrive in the Yemeni capital of Sanaa, UN officials said, after the easing of a nearly three-week-old military blockade that caused an international outcry.

International aid groups have welcomed the decision to let aid in, but said aid flights are not enough to avert a humanitarian crisis.

About seven million people face famine in Yemen and their survival depends on international assistance.

UNICEF said one flight carried "over 15 tonnes" of vaccines that will cover around 600,000 children against diphtheria, tetanus and other diseases.

"The needs are huge and there is much more to do for #YemenChildren," the world body said on its Twitter account.

A flight carrying eight employees of the International Committee of the Red Cross had also landed.

The Saudi-led coalition fighting the armed Houthi movement in Yemen said on Wednesday it would allow aid in through the Red Sea ports of Hodeidah and Salif, as well as UN flights to Sanaa, but there has been no confirmation of any aid deliveries yet.

A spokesman for the US-backed coalition said in a statement issued yesterday that 82 permits have been issued for international aid missions since 4 November, both for the Sanaa airport and Hodeidah, the country's main port where some 80% of food supplies enter.

"That includes issuing clearance for a ship today (Rena), carrying 5,500 metric tonnes of food supplies, to the port of Hodeidah," a coalition spokesman said in a statement issued in a status update published by the Saudi embassy in Washington.

However, officials at the port said today that no ships have arrived yet and they were not expecting any to dock soon.

The coalition closed air, land and sea access in a move it said was to stop the flow of arms to the Houthis, who control much of northern Yemen, from Iran.

The action came after Saudi Arabia intercepted a missile fired toward Riyadh. Iran has denied supplying weapons.

The blockade drew wide international concern, including from the United States and the United Nations secretary-general.

The heads of three UN agencies had earlier urged the Saudi-led military coalition to lift the blockade, warning that "untold thousands" would die if it stayed in place.