Income for some groups has dried up so much that they now fear their work for the most vulnerable will have to stop.

Gifts of food and money from the public have also fallen, with some organisers citing "donation fatigue" after the bushfires.

On top of that, panic buying of the cheapest food in supermarkets has left little on the shelves for the very poorest in society, according to one Canberra charity leader.

Income is drying up in different ways. St John Ambulance, for example, charges organisors of big events for the medical aid its volunteers give but numerous cancellations now means money won't come in.

St John Ambulance in the ACT had lost $33,000 in the last few days from cancellations, according to chief executive, Bianca Russell. The organisation also runs first-aid courses for companies and these were being cancelled.

St John Ambulance receives no government funding and Bianca Russell said that without income its future was threatened - and just after its substantial spending to help bushfire victims.

She was dismayed that big commercial organisations were already seeking tax-payers' help but the plight of charities wasn't getting the same attention. Prime minister Scott Morrison recently poured cold water on a bail-out for the NRL.

"Big business is reaching out to the government for assistance. It would be a pity if they got support while small people without such a loud voice were overlooked," she said.

Anglicare is also feeling the pinch. "We have definitely noticed a downturn in donations following the incredible help we received during the bushfires," manager Amy Lanham said.

Demand is about to rise. "Winter clothing and heating costs put additional pressure on families already struggling." She encouraged people to keep giving to charities which helped the worst-off in society.

The St Vincent de Paul Society is also under pressure. Its national fund-raiser on June 18 brought in $8 million last year. In Canberra, prominent people sleep out in the open to highlight the plight of the homeless. They also give money. At the moment, the event is on but in doubt.

The run on food in supermarkets is also hurting the poor, according to Barnie van Wyk, the chief executive of Vinnies in Canberra and Goulburn.

Fearful shoppers were buying cheap items and not leaving enough on the shelves for even poorer people. "There is often not much left for those who can only afford to purchase essentials on a week-by-week basis," he said.

Normally generous people were now worried about their own situation because of the coronavirus and concern for the vulnerable was taking second place.

All the charities are trying to maintain services as money gets tighter.

St John Ambulance, for example, is still giving first-aid courses to youngsters but training in mouth-to-mouth resuscitation using mannequins has been stopped.