United Nations human rights activist chief Zeid Ra'ad al-Hussein have expressed concern that the Saudi Arabia and United Arab Emirates-led military operation in Yemen could endanger millions of civilians, as the coalition continues to pound Houthi fighters in the port of Hudaida.

He was speaking at the opening session of the UN Human Rights Council in Geneva, where he gave an overview of the overall human rights situation, while denouncing the threat of growing "chauvinistic nationalism" around the world.

On Monday, coalition Apache attack helicopters pounded Houthi positions, as civilians fled in search of shelter from the biggest battle of the war in three years.

The attack reportedly targeted Houthi snipers and fighters positioned on the rooftops of schools and homes in the Manzar neighbourhood near Hudaida's airport compound, residents said, in fighting that has wounded dozens of civilians and prevented aid organisations from reaching parts of the city.

While most of the intense fighting is in Hudaida, Houthi media reported over 40 air strikes in other parts of Yemen in the past 24 hours.  

Losing Hudaida would seriously weaken the Houthis by severing supply lines from the Red Sea to their stronghold in the capital Sanaa, and depriving an estimated 70 percent of the population access to food and medicine. 

It could also give an edge to the Western-backed Saudi and UAE-led coalition that, despite superior weaponry and firepower, has failed to defeat the Houthis in a war that has killed 10,000 people and created the world's most urgent humanitarian crisis.

The battle for Hudaida, launched six days ago, could drag on, inflicting more suffering on civilians who have already endured air raids, port blockades, hunger and a cholera epidemic.

In a post on social media late on Sunday, Anwar Gargash, the UAE's minister of state for foreign affairs, said that a coalition victory in Hudaida "will pull the Houthis back to the negotiating table"