War-torn Yemen is on the brink of famine, with millions of women and children most at risk of starvation, the United Nations says.

Recent fighting around major ports has stalled the importation of food and other humanitarian aid.

UN under-secretary-general for humanitarian affairs Stephen O'Brien pleaded with the UN Security Council to increase humanitarian assistance to the country.

"I was shocked by what I saw. The civilian population is bearing the brunt of the conflict," he said after recently returning from Yemen.

"A shocking four out of five Yemenis require humanitarian assistance, and nearly 1.5 million people are internally displaced."

Yemen has been torn apart by months of fighting between Houthi rebels, backed by Iran, and forces loyal to the exiled government, with support from Saudi Arabia.

Key points: UN says millions at risk of starvation

UN says millions at risk of starvation Aid agencies say conflict is a "children's emergency"

Aid agencies say conflict is a "children's emergency" Calls for international community to ramp-up aid efforts

Mr O'Brien called on the international community take immediate action to try and secure a peace deal in the country.

"We must get the parties to stop the fighting and return to the negotiating table before it's too late," he said.

"Otherwise there will be nothing left to fight for."

Aid agencies are just starting to trickle into Yemen.

"Right now we are seeing this crisis almost reaching breaking point," Save the Children's Mark Kaye said.

"I mean, there is an absolute climate of fear. Families are really, really worried about where this is going.

"Just yesterday one of my colleagues lost his house, it was completely burnt down in an area outside of Sanaa that had been in fierce fighting."

Save the Children says the conflict is a "children's emergency". ( AFP: Mohammed Huwais )

More than 1,000 children killed or injured: Save the Children

The civil war has killed more than 4,300 people, many of them civilians.

Much of the country has been blocked off to foreign journalists and observers and it has been extremely difficult to gather information on how Yemenis are coping with the fighting.

"What you see is huge great big queues of cars waiting for fuel," Mr Kaye said.

"I'm talking four wide kilometres deep as people wait for what limited fuel there is on the market right now.

"Gas is extremely important for these families to cook, prices have now doubled."

Save The Children said more than 1,000 children have been killed or injured in the fighting in Yemen and the number of young people recruited or used as fighters is increasing.

"We really see this as a children's emergency," Mr Kaye said.

"Every day children are going hungry, they are going thirsty, they have been displaced from their homes, they are being forced out of school."

The World Food Program said 13 million people in the impoverished Arab state, half the population, are hungry, while 6 million face starvation and urgently need food aid.

"It means that families are going to bed not knowing where their next meal is going to come from tomorrow," Mr Kaye said.

"Yemen is largely a forgotten crisis. The large scale, the huge numbers don't seem to be getting much coverage."

Aid agencies say only 18 per cent of funding needed to address immediate needs in Yemen has been received.