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Sufra
Food banks say they have a shortage of basic items because shoppers are stockpiling as fears grow over the spread of coronavirus.
London food bank Sufra, which donates 3,000 food parcels annually, said cheap items such as pasta, rice and tinned goods were proving hard to obtain.
Another food bank in the capital said its donations were down by 25%.
The Trussell Trust said it hoped the "generous public" would continue donating.
"We're working with our network on how best to support people as the situation unfolds," the food bank charity added.
The North Paddington Foodbank (NPF) in London said donations were down by 25% meaning it had to spend an additional £200 per week to top up supplies.
But manager James Quayle said finding supplies has been difficult.
"Both of those have been restricted over the last couple of weeks because the items we are trying to purchase may not be available [from supermarkets]," he said.
"We've been hit quite hard by it to be honest."
One of their regular food bank users, King Anthony Sarkar, from Paddington, said: "I couldn't manage life without it. Tinned foods, rice and pasta, everything here makes a meal.
"You get a meal all the time."
Mr Quayle said he was concerned they could have to close their doors and run a delivery service only to those in greatest need.
His experience was echoed by Rajesh Makwana, from the Sufra food bank in north-west London, who said 40% of its users are refugees or asylum seekers who rely on the food banks as they are not allowed to work.
It has put out an emergency appeal for donations after receiving fewer items from its collection points at schools, churches and local small businesses.
Mr Makwana confirmed they had also struggled to buy staple items from their normal outlets as supermarkets ran out of these cheaper items due to the public buying more than normal.
"The families we support simply can't afford to panic buy and hoard food, they're already knocking on our door in search of basic supplies," he said.
Mr Makwana said the charity had now started rationing things like pasta and toiletries.
Like NPF, Sufra is also looking at running a delivery-only service in order to protect volunteers from cross-contamination.
Mr Makwana said goods were being pre-packaged into parcels to prevent germs spreading.
"We want to provide a service but we're struggling on so many fronts," he added.