A Saudi-led assault on the vital Red Sea port city of Hodeidah in Yemen is threatening the lives of the rebel held city’s 600,000 people who rely almost entirely on imported food, medicine and fuel.

As Arab forces bombard Hodeidah, which is held by the Iranian-aligned Houthis, the UN and aid agencies have warned that one of the world’s worst humanitarian catastrophes is unfolding.

The UN Security Council has called for the Hodeidah port to be “kept open” while apache attack helicopters bombed a strip of the coastal territory near the city’s airport on Friday.

The Yemen port is the main supply route bringing food and resources to the Arab nation’s 8.4 million people, who are already suffering malnutrition and disease after more than three years of conflict in Yemen.

Save the Children humanitarian affairs head Nicola Krey told The New Daily if the port was cut off, humanitarian aide would not be able to get to affected populations.

“What we’re going to see is huge civilian casualties, impacts to infrastructure and a stop on life saving aide getting to that country,” Ms Krey said.

While tens of thousands of Yemenis scramble to flee Hodeidah, Arab forces have closed off the main road linking the port city to the capital, Sanna, to block reinforcements.

United Nations Obedi Salem Al Zaabi told reporters in Geneva on Friday coalition forces were also just two kilometres away from Hodeidah’s airport.

Oxfam Australia’s country director in Yemen, Muhsin Siddiquey told the ABC’s Radio National program more than 90 per cent of food is imported into Yemen and 70 per cent of that food is imported through the port of Hodeidah.

Mr Siddiquey said Hodeidah residents were already fleeing to safety, but few knew how to escape.

He estimated 250,000 people could “lose everything” in “complete destruction” and 350,000 people may be displaced.

“If the port is not fully functional and if somehow Hodeidah is taken over…if the lifeline is cut off, then people will not have food,” he said.

“There will be more hunger, more deaths and families will have to be ready to bury their beloved ones.”

Aid agency Save the Children Yemen country director Tamer Kirolos estimates 300,000 children’s lives are a risk, caught in the crossfire and beyond the reach of humanitarian aide or medical care.

“The battle for Hodeidah will almost certainly result in a huge loss of civilian life and damage to vital infrastructure,” Mr Kirolos said.

United Arab Emirates Ambassador to Australia Obaid Al Heri Salem Ketbi said in a statement the UAE and other Arab Coalition partners had launched military action at the request of Yemen’s government.

Dr Al Ketbi said the Houthis had exploited the control of Hodeidah and they had used the port as a source of finance as well as smuggling arms and ballistic missiles, interfering with aid to the Yemini people.

He said a comprehensive aid delivery strategy would follow military action with support for people in Hodeidah city.

“We will establish direct shipping lanes to ensure aid starts arriving as soon as possible,” he said.

The Saudi-led forces have been struggling to unseat the Houthis and restore an exiled Saudi-backed government to halt what is considered to them as ‘Iranian expansionism’ since 2015.

Ousted Yemeni president Abd-Rabbu Mansour Hadi, who lives in Saudi Arabia, arrived in Aden on Friday (Thursday local time) in his first trip to the southern city in more than a year.

“Our imminent victory in Hodeidah will be the …gateway to retrieving our kidnapped capital and exert the influence of the government over every inch of the country,” he said.