Police patrol a main street in downtown Harare, Zimbabwe, ahead of expected protests on Tuesday. (Associated Press)

The UN's World Food Programme warns that it will have to cut food rations for hungry people in Zimbabwe this month in order to make its stretched resources go further.

The relief agency reports that it will have to feed four million people in November, compared with the two million people who received rations in October, the first month it was operating on a large scale in the country during the current crisis.

Because of the cuts, each person will now receive a cereal ration of 10 kilograms per month, down from 12 kilograms, and one kilogram of pulses (a porridge made of peas or beans) per month, down from 1.8 kilograms.

Emilia Casella, a spokeswoman for the World Food Programme, says the situation will only get worse, because the agency has not received any funding commitments to cover relief for the country past December.

"There is currently no food in the pipeline for distributions in January and February, and we expect in the early part of 2009 that the number of people in Zimbabwe who will need assistance will reach 5.1 million people," Casella said.

That would amount to 45 per cent of the country's population.

Not a single dollar has been pledged for Zimbabwe, though the agency had appealed for $140 million US from donors around the world to cover the first three months of 2009.

Casella said Zimbabweans are resorting to drastic measures in order to survive in the face of an economic collapse that put seeds and fertilizer out of the reach of many subsistence-level farmers.

Their plight has been made worse by poor growing weather and the fact that AIDS has sapped the workforce of labourers.

Casella said many people are surviving on only one small meal a day or eating wild foods, and hungry families are being forced to exchange their precious livestock for buckets of corn.

If money is pledged for the relief effort, it will still take six to eight weeks to put the wheels in motion to get the new food aid to the country, she added.