Arab troops appeared poised to enter the airport of Yemen's main port, Hodeidah, on Friday as a Saudi-led alliance prepared to seize the city in the biggest battle of a three-year war.

Coalition warplanes pounded coastal areas southeast of the Houthi-held city as residents gathered at dawn in an open area where Eid al-Fitr prayers are held each year to mark the end of the holy fasting month of Ramadan.

"Many warplanes were flying low over the city during the prayers," one resident of the heavily defended city said.

Alliance forces led by Emirati troops have advanced to within metres of the airport, entering the al-Manzar area adjacent to it, Saudi-owned Al Arabiya television quoted Yemeni military officials as saying.

Warplanes also struck the main road linking Hodeidah to the capital Sanaa to block reinforcements to the Houthis, the Iran-aligned movement that controls the capital and most of Yemen's populated areas.

The United Nations is struggling to avert disruption to Hodeidah port, the main lifeline for food aid to a country where 8.4 million people are facing starvation. A UN diplomatic source said five commercial vessels were offloading at the port.

"I urge all parties to the conflict to meet their obligations to protect civilians and civilian infrastructure and take active steps to respect international humanitarian law," David Beasleye, executive director of the UN World Food Programme, said in a statement.

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