The Chancellor’s move will come after Prime Minister Boris Johnson told Parliament he wanted to achieve "parity of support" so self-employed workers could have similar levels of protection to waged workers amid the epidemic.
Mr Sunak will outline his emergency measures later, on the same day the number of people who have tested positive for Covid-19 is likely to pass 10,000 after cases increased by almost 1,500 on Wednesday.
Those recently diagnosed include the Prince of Wales, who is self-isolating in Scotland with what Clarence House described as "mild symptoms".
Also on Wednesday, the Foreign Office announced that Steven Dick, 37, the deputy head of mission at the British Embassy in Budapest, had died after contracting coronavirus.
Meanwhile, more than 400,000 people volunteered to help the health service during the crisis in just 24 hours after the PM appealed for 250,000 to help out.
As the Commons shut down early for Easter due to the escalating crisis, Mr Johnson told MPs: "There are particular difficulties with those who are not on PAYE schemes as ... I think the whole House understands.
"We are bringing forward a package to ensure that everybody gets the support that they need."
He added: "I cannot, in all candour, promise the House that we will be able to get through this crisis without any kind of hardship at all.
"We will do whatever we can to support the self-employed, just as we are putting our arms around every single employed person in this country."
Ahead of the Chancellor's announcement, The Daily Telegraph reported one in three self-employed workers were set to ask the Government to support their wages.
The move comes after Mr Sunak set out plans for 80 per cent wage subsidies for PAYE employees last week.
It should affect 1.7 million of the five million self-employed, according to the same newspaper.
The Government is also under pressure to provide more protective equipment for doctors and nurses, with the number of positive UK tests rising to 9,529 at 9am on Wednesday, up from 8,077 at the same point on Tuesday.
A total of 97,019 people had been tested with 87,490 negative results, while the number of deaths of UK patients who tested positive for Covid-19 increased from 422 to 463.
The British Medical Association (BMA) warned doctors and patients would die without adequate personal protective equipment (PPE) across the NHS.
It said said there was "growing evidence that thousands of GPs and hospital staff are still not being provided with the kit they need to properly protect themselves and their patients", despite Government assurances.
Health Secretary Matt Hancock has said millions of items of PPE had been sent out in recent days, with a hotline set up so staff could report shortages.
BMA council chairman Dr Chaand Nagpaul said: "A construction worker wouldn't be allowed to work without a hard hat and proper boots.
"Even a bee-keeper wouldn't inspect a hive without proper protective clothing.
"And yet this Government expects NHS staff to put themselves at risk of serious illness, or even death, by treating highly infectious Covid-19 patients without wearing proper protection. This is totally unacceptable."
Asked about the latest death toll figures, business minister Nadhim Zahawi told BBC2's Newsnight: "Well, at this stage I wouldn't interpret anything into the figures.
"I think the Prime Minister is right to say that the message is very clear - stay at home, make sure we protect the NHS and save lives."
Housing Secretary Robert Jenrick told ITV's Peston: "We need to get more PPE out to people working on the frontline, that's in hospitals, it's in social care, it's in pharmacies and GPs' surgeries.
"We are doing that, we are ramping up efforts very significantly, we're taking very large stocks now, over 10 million masks for example in the last few days.
"Every social care provider in the country will get deliveries this week. We now have a PPE hotline so that those people on the front line can ring up, get the order that they desperately need."
The economic impact of the outbreak has also brought a large spike in the number of people applying for Universal Credit.
Ministers are being urged to step-up testing for coronavirus, especially among health workers.
But the UK's chief medical officer dismissed suggestions a coronavirus antibody test will be ready to buy online next week.
Professor Chris Whitty said the accuracy of the tests needed to be properly tested before they were made available, and he stressed that frontline NHS workers would need them first so they could get back to work if they have already had the virus.
A national salute is set to take place to honour the hardworking NHS staff who are trying to battle coronavirus.
In a gesture of thanks to the frontline healthcare heroes, everyone across the nation has been invited to join a a mass round of applause from their doorsteps, windows and balconies on Thursday at 8pm.