Residents in Yemen's Red Sea port of Mokha began escaping the city on Friday, as security forces prepared to engage in a long-awaited battle with Houthi rebels.

Hundreds of families were allowed to exit the rebel-held port city to head further north towards Hodeida, leaving what some described as a newly-established "military zone".

"If the Houthis don’t withdraw from Mokha, I think they will wreck everything as they are spread out everywhere," one resident who chose to flee told UAE's The National.

But the resident confirmed many others had chosen to remain in the city - where the rebels imposed a 9pm curfew - "because they have nowhere else to go and they don’t want to live in a camp for the displaced, so they are stuck inside the city," he said.

Among those fleeing the battle zone are Houthis who sold their weapons and donned civilian clothing to merge between the crowds, he suggested, as Saudi media reported pro-government forces and some 500 armoured military vehicles stood just 10 kilometres away from the port city.

On Friday, Saudi-led coalition airstrikes hit two military camps, an ammunition depot and an arms transporter in the Red Sea coast Hodeida province, military sources said, killing at least 29 rebels and wounding 20.

Rebels control nearly all of Yemen's Red Sea coast to the north and last year targeted both US warships and a United Arab Emirates vessel contracted to the Saudi-led coalition with rocket fire from the area.

The United Nations has stepped up peace efforts this week with UN envoy Ismail Ould Cheikh Ahmed meeting Hadi at his base in second city Aden on Monday.

The envoy has been pushing a peace plan that would see a restored ceasefire leading to a political transition under which Hadi's powers would be significantly reduced.

The push for a negotiated settlement has been driven by mounting civilian casualties.

At least 10,000 people have been killed in Yemen's ongoing civil conflict since the Saudi-led coalition began its military intervention in March 2015, the majority in coalition airstrikes.