The United Nations has pledged $6.5 billion to Syria to deal with the worsening humanitarian crisis in the region.

The financial aid, which aims to help over 16 million struggling people in the region, is the largest ever humanitarian assistance package by the UN.

"This is the largest amount we have ever had to request at the start of the year," Valerie Amos, UN under-secretary-general for humanitarian affairs said in a news conference.

The Syrian emergency aid constitutes over half of the UN's total funding plan of $12.9 billion for 2014, which aims to help about 52 million people around the world.

Nearly three-quarters of Syria's 22.4 million population will require humanitarian aid in the coming year, according to UN estimates.

The UN food agency is expanding emergency operation to increase food coverage, as an assessment by the World Food Program shows that about half the Syrian population are experiencing food shortages.

The cost of staples is expected to spiral upwards, coupled with limited access to clean water in many districts. Bread prices have reportedly risen by 500% in some areas.

A recent report by the International Rescue Committee warns that the threat of starvation is dangerously real in Syria.

Speaking in Geneva, Amos expressed grave concern over "millions of Syrians who are displaced and in urgent need of food, shelter and healthcare both inside the country and across the region."

Relief groups say that aid is frequently held up at Syria's borders, or hardly reaches people living in battle zones and war-ravaged communities.

Neighbouring countries of Egypt, Iraq, Jordan, Lebanon and Turkey will also receive UN aid of up to $4.2 billion to assist Syrian refugees, while food aid in the form of cash and vouchers will also be provided to host communities.

The UN estimates that 250,000 Syrians encircled by government forces are battling a severe winter, and are deprived of basic services and amenities. The situation is expected to be even bleaker for about 45,000 people living in the two northern towns controlled by Jihadi rebels.

The two-and-a-half-year conflict has led to a near-collapse of economy in Syria, especially in the contested zones.

USA Today reports that in addition to 2.3 million Syrians who have already fled the country over the two years of war, there are about 6.5 million internally-displaced people.

Basic medical items such as antibiotics, painkillers and gauze are in short supply in many districts, according to a New York-based aid group, International Rescue Committee.

Syria recently reported the country's first cases of polio since 1999. The outbreak has left 10 children paralysed and poses a threat to hundreds of thousands of others. Immunisation programmes have been largely neglected in the country since the civil war broke out more than two years ago.