Yemen is in the grip of an unprecedented cholera epidemic that is killing one person nearly every hour.

The Saudi-led coalition has closed the country's main airport and prevented many reporters and human rights workers from entering Yemen.

But the evidence from local journalists and aid agencies on the ground is clear — more help is urgently needed.

Abdo Ibrahim is still in a state of shock. A few hours ago, he thought his eight-year-old son Muhab was about to die in his arms.

Abdo Ibrahim thought his son was about to die in his arms, he is still in a state of shock. ( Supplied: Moohialdin Fuad )

"As I was on my way to the hospital I thought he's dying. He was so weak. I said, 'That's it, it doesn't look like he will live'," Mr Ibrahim, said.

"His eyes had rolled back into his head and I thought, 'I've lost my child! He's dead, dead'."

Cholera is an acute diarrheal infection caused by contaminated food or water.

It can kill children within just a few hours.

"Last night at 10pm he was fine," Mr Ibrahim said. "But in the morning he couldn't even stand up."

Thanks to his father's quick decision to bring him to the hospital, Muhab survived, but across Yemen one person each hour is now dying from cholera.

Muhab was one of the lucky ones who has survived the deadly illness. ( Supplied: Moohialdin Fuad )

'The worlds worst humanitarian disaster': UN

The UN says the death toll from the outbreak that began in April has now surpassed 800. A quarter of the dead are children.

"The number of casualties is increasing day-by-day," said Dr Ismail Mansoury, a paediatrician at Sanaa's Al Sabheen hospital.

"The cholera spreads fast because we are in a society where it's hard to live healthy."

The hospitals in Yemen are so full patients are being treated in tents in the car park. ( Supplied: Moohialdin Fuad )

Yemen is the Middle East's poorest country. A Saudi-led multinational coalition — backed by the US and UK — has been bombing Yemen for the past two years after Iranian backed Houthis rebels took over the capital Sanaa in 2015.

The fighting, combined with a Saudi blockade on the country, has left 7 million people here on the brink of starvation.

"It's become really hard to get proper food now in Yemen," Mr Ibrahim said.

"The reasons it's so hard is because we don't have much money. Honestly our daily income is so low. That's why many parents can't buy their kids quality food."

The UN says Yemen is now the world's worst humanitarian disaster.

"The health system is about to collapse," UNICEF Yemen's Meritxell Relano said.

"With health workers who have not received a salary. With half of the facilities being closed and with very limited supplies coming into the country."

Local workers warn the epidemic is "at devastating proportions" and is set to get worse. ( Supplied: Moohialdin Fuad )

Australia has given $10 million to Yemen since the crisis began.

Aid agencies say the Government needs to be more generous, at a time when our foreign aid spending is already at a record low.

"The cholera epidemic is really at devastating proportions and will only get worse," said Dr Nicole Bieske, humanitarian policy adviser at Oxfam Australia.

"And as that situation continues, we call on the Government to consider giving more funding."

Oxfam is calling for an immediate ceasefire to allow relief workers to try to halt cholera's deadly spread.