UN aid convoys with enough supplies to last a month have arrived at a besieged Syrian town where residents have been forced to eat cats and dogs because of a food shortage.

Crowds including women and children waited for the convoys at the town's main entrance.

"Our children are dying of hunger," a schoolteacher said.

Madaya, once a popular holiday resort for Syrians, has been blockaded by government troops and their allies for six months.

Food, blankets and medicine were also dispatched to the villages of Foua and Kfarya in Idlib province, under siege by rebels seeking to oust President Bashar al-Assad.

Vehicles carrying the much-needed aid from the International Committee of the Red Cross left Damascus earlier.

Thousands of people are facing starvation because of major shortages in the areas. Many have said they have no food, water or electricity.

The aid group Doctors Without Borders said 23 patients had died of starvation at a health centre it supports in Madaya since December 1st - including six children under the age of one.

The operation was approved last week after the Syrian government said it would now allow aid into the affected areas.

A picture posted on a Facebook page last week detailing the suffering in Madaya showed a picture of of someone seemingly preparing to slit the throat of a cat - alongside the caption read: "Because it's just what's left for us".

An unnamed aid worker in the town confirmed that some residents were eating cats and dogs to survive, while others ate leaves.

"Humanity has fallen with the fall of the first man from hunger in Madaya," he said.

Families were also said to have been forced to eat grass and drink water flavoured with jam or spices.