Fighting continued to rage on the outskirts of Yemen's largest port, Hudaida, near the city's airport while the UN made a desperate plea for both sides to exercise restraint.
Forces from a Saudi-led coalition were poised to enter the airport of Yemen's main port, Hudaida, on Friday as the Saudi-led alliance prepare to try to seize the city from Houthi rebels in the biggest battle of a three-year war.
Coalition warplanes pounded coastal areas southeast of the city as residents marked the end of the holy fasting month of Ramadan by gathering at dawn in an open area for Eid al Fitr prayers.
"Many warplanes were flying low over the city during the prayers," one resident of the heavily defended city said.
Forces of the western-backed coalition, led by Emirati troops, have advanced to within metres of the airport, Saudi-owned Al Arabiya television quoted Yemeni military officials as saying.
Warplanes also struck the main road linking Hudaida 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.
Details of casualties were not immediately known, but AFP reported that heavy fighting had left at least 39 people dead on Thursday, a day after the assault on Hudaida began.
The Houthis suffered 30 fatalities on Thursday in the clashes, medical sources told AFP.
Nine pro-government troops were killed in the same area, the medics said. Military sources said the deaths were caused by mines and snipers.
An AFP correspondent south of Hudaida airport reported seeing ambulances evacuating dead and wounded government loyalist fighters as reinforcements headed towards the front line.
The United Arab Emirates, a driving force in the coalition, said four of its troops were killed on the first day of the offensive.
The United Nations, which says the war has created the world's most pressing humanitarian crisis, is struggling to avert disruption to Hudaida.
The port is 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's World Food Programme, said in a statement.
Capturing Hudaida would give the Saudi-led coalition the upper hand in the war, in which neither side has made much progress since the coalition intervened in 2015 to restore the internationally recognised government in exile.
Many residents have fled the city.
"My family left for Sanaa yesterday but I stayed behind alone to protect our home from looters," said Mohammed Abdullah, an employee of the Houthi administration.
The United Nations says 22 million Yemenis need humanitarian aid and the number at risk of starvation could more than double to more than 18 million by year-end unless access improves.
Coalition leaders Saudi Arabia and the United Arab Emirates say there are plans to prevent the battle from worsening the humanitarian disaster and they will be able to improve food supplies once they control Hudaida, the Houthis' only port.
Riyadh and Abu Dhabi say the Houthis are a proxy force for Iran, Saudi Arabia's arch regional rival.
The Houthis, from a Shia minority, deny being Tehran's pawns and say they took power in a popular revolt and are defending Yemen from invasion by its neighbours.
Houthi leader Abdel Malek al Houthi called on his followers late on Thursday to head to the frontlines to fight the "instruments of the United States and Israel."
"The Yemeni coast has been a strategic target for the invaders throughout history and confronting the aggression is a national duty in the face of the danger of foreign occupation."
The Western-backed alliance says capturing Hudaida would deprive the Houthis of their main source of income and prevent them from bringing in missiles, dozens of which have been fired at Saudi Arabia.
The United States and other Western powers provide arms and intelligence to the coalition. Human rights groups criticise them over air strikes that have killed hundreds of civilians.
The United States rejected a request from the UAE for intelligence, mine-sweeping and airborne intelligence, surveillance and reconnaissance (ISR) assets for the Hudaida operation, a UAE official said, speaking on condition of anonymity, while noting congressional opposition.
However, the official said France had agreed to provide mine-sweeping support for the operation. The UAE has said the Houthis could plant land and sea mines at the port.
Arab league support for assault
The Arab League said it supported the coalition, especially in Hudaida. The Gulf initiative, national dialogue and UN Security Council decisions are the basis for a political settlement, it said after an emergency meeting in Cairo.
The war in Yemen is one of several regional conflicts that pit allies of the Sunni Muslim Arab states against forces aligned to Shia Iran.
After a two-hour UN Security Council meeting on Thursday, the 15-member body urged "all sides to uphold their obligations under international humanitarian law," said Russian UN Ambassador Vassily Nebenzia, president of the council for June.
"They were united in their deep concern about the risks to the humanitarian situation and reiterated their call for the ports of Hudaida and Salif to be kept open," Nebenzia told reporters.
Houthi leader Mohammed Ali al Houthi has blamed the West for the assault, "The British told us a week ago that the Emiratis and the Saudis had told them they would not enter the battle of Hudaida without their agreement and assistance."
A Houthi statement warned commercial ships in the Red Sea, one of the world's most important trade routes, to stay 32 kilometres (20 miles) from coalition warships or potentially face attack.