The United Nations said Monday it has started delivering chemicals to treat water consumed by more than 10 million people in Syria, nearly half of the strife-torn country's population.

The first four trucks carrying 80 tonnes of such chemicals including sodium and chlorine crossed through the Jordanian border into Syria on Sunday heading for war-torn regions of Homs, Aleppo, Hama and Idlib, the UNICEF said.

It said it will deliver another 1,000 tonnes of chlorine in coming weeks to cities and communities across all 14 governorates of Syria.

"This shipment is very timely as supplies of chlorine in Syria have fallen dangerously low, making access to safe water challenging for many families," said Youssouf Abdel-Jelil, UNICEF representative in Syria.

"This puts the population -- and children especially -- at high risk of contracting diarrhoea and other water-borne diseases."

UNICEF said its ongoing work comes amid rising concern over the impact of Syria's 22-month conflict on water pumping stations and other vital infrastructure as well as the implications for children's health in particular.

"Reports say that the quality and quantity of water supplies continue to deteriorate in different parts of the country and in some areas very severely," UNICEF said.

UNICEF needs $22.5 million to deliver life-saving assistance in Syria in the area of water and sanitation from January to June 2013. Only $4.8 million has been received so far, according to the organisation.