A recent Huthi rebel advance near Yemen's lifeline port of Hodeida has displaced more than 6,000 people, the United Nations has said.

The insurgents on Friday took control of a large area south of Hodeida, a key port where the warring sides agreed a ceasefire in 2018, after loyalist forces withdrew.

"Some 700 families (approximately 4,900 people) were displaced" to Khokha, over 100 kilometres (60 miles) south of Hodeida, "while 184 other families (about 1,300 people) were displaced further south" to the Red Sea coastal town of Mokha, the UN Office for the Coordination of Humanitarian Affairs (OCHA) said, citing Yemeni government sources.

"No displacement has been reported within the areas that came under control of the de facto authorities," it said in a statement Sunday, referring to the Huthis.

Citing aid partners on the ground, it said a 300-tent site for displaced people had been set up in the Khokha district, while the authorities were reportedly looking for another site to cope with the influx.

But the UN also said the Huthi advance could result in "improved movement for civilians" between the provinces of Hodeida and Sanaa, and along roads connecting Hodeida city with other districts.

The Hodeida ceasefire was agreed at Yemen's last peace talks in Sweden in 2018, but clashes have since broken out between the rebels and pro-government troops around the city.

Two military officials told AFP that fighting also erupted Saturday when the rebels tried to push farther south into government-controlled territory, but loyalist forces repelled the advance.

A Saudi-led coalition intervened in Yemen in 2015 to shore up the government, a year after the Huthis seized the capital Sanaa.

Tens of thousands of people, mostly civilians, have been killed and millions displaced, in what the UN calls the world's worst humanitarian crisis.

The Iran-backed insurgents have also been engaged in a sustained attempt to capture Marib, the government's last stronghold in the north.

The UN last week called on "all parties to the conflict to ensure the safety and security of civilians in and around those areas where shifts in frontlines have taken place".