* Coalition troops storm airport in key Houthi-held port
* Fighting engulfs main coastal road leading to city centre
* UN peace envoy leaves capital Sanaa without comment
* Red Sea port is lifeline for millions of Yemenis
* UN unloading three food aid ships in Hodeidah harbour



Arab coalition troops stormed the airport in Yemen's main port Hodeidah on Tuesday and captured large areas of the compound in battles with Iran-aligned Houthis, a Yemeni military source, the UAE news agency and local residents said.
Residents of the strategic Red Sea city said battles were also raging on the coastal road leading to the densely populated city centre from the airport, with Apache helicopter gunships of the Western-backed coalition providing close air support.
Wresting the airport from the Houthis would be a major step towards a takeover of Hodeidah by coalition-backed forces. Saudi Arabia and the United Arab Amirates have pledged a swift assault to avoid disrupting aid deliveries to Yemen through the port.
"We can hear the sounds of artillery, mortars and sporadic machinegun fire. The Houthis have been using tanks," a resident close to the coastal strip told Reuters by telephone, asking not to be identified.
"Water has been cut off to many of the areas near the Corniche area because the Houthis have dug trenches and closed water pipes. Many people are fleeing these neighborhoods and going deeper into the city centre."
Saudi and UAE state media accused the Houthis of shelling civilian districts. Residents said the Houthi tanks were targeting coalition forces.
The Arab alliance launched the onslaught on Hodeidah, the Houthis' sole port, on June 12 to try and turn the tables in a long-stalemated proxy war between Saudi Arabia and Iran that has exacerbated turmoil across the Middle East.
"They have stormed the airport," an anti-Houthi Yemeni military source told Reuters earlier on Tuesday.
The UAE state news agency WAM said large swathes of the airport compound had been taken by coalition forces. Houthi media said coalition warplanes had carried out more than 40 strikes on the airport since the morning.
The escalation in fighting has wounded and displaced dozens of civilians and hampered humanitarian agencies trying to send vital aid to million of Yemenis via the Red Sea port.

"Terrified"

Tuesday's battles spread panic among local inhabitants.
"My children are terrified. The fighting and the sounds of explosions are everywhere and we are stuck in our house in the district of Rabsa with no running water," Iman, a 37-year-old mother of two, said tearfully.
"What have we done for all of this?”
Mohamed Sharaf, 44, a civil servant, said he had sent his entire family to Sanaa, the Houthi-held inland capital, several days ago and he was getting ready to leave himself. "There is death and destruction everywhere in this city.”
The United Nations fears the offensive will worsen what is already the world's most urgent humanitarian crisis, with 22 million Yemenis dependent on aid, and an estimated 8.4 million believed to be on the verge of starvation.
UN officials estimate that 600,000 people live in and around Hodeidah and that in a worst-case scenario the battles could cost up to 250,000 lives. A senior UN humanitarian official told Reuters a main determinant in arriving at that estimate was the risk of a cholera outbreak.
The war has killed more than 10,000 people in all.
Hodeidah port remained open on Tuesday with the UN World Food Programme hastening to unload three ships containing enough food for six million people for one month, WFP spokeswoman Bettina Luescher told reporters in Geneva.
UAE Minister of State for Foreign Affairs Anwar Gargash said on Monday the coalition was taking a measured approach to minimise risks to civilians, and allowing the Houthis an escape route inland to their bastion in Sanaa.
The Arab states say their aim is to seize the airport and port quickly and avoid street battles in the city centre. But the Houthis were well dug into Hodeidah as it constitutes the key supply line to territory they control including Sanaa.
Martin Griffiths, UN peace envoy for Yemen, returned to Sanaa on Saturday, four days after the coalition assault on Hodeidah began, in an apparent effort to dampen hostilities. But he departed on Tuesday without comment, witnesses said, leaving unclear whether any headway was made.
A member of the Houthis' ruling politburo, Mohammed al-Bukhaiti, denied Gargash's assertion that the talks with Griffiths had focused on handing over Hodeidah "because this request is unrealistic".
"During all his visits, the envoy has discussed a comprehensive political solution that addresses...all fronts and not only Hodeidah," he told Reuters by telephone.
The coalition intervened in Yemen's war in 2015 to try and unseat the Houthis, restore the internationally recognised Yemeni government in exile and thwart what Riyadh and Abu Dhabi see as Iran's expansionism in the region.
The Houthis, who control the most populated regions in the chronically unstable nation of 30 million people, deny they are puppets of Iran. They say their movement reflects a popular revolt against state corruption and aims to protect Yemen from foreign invasion.