Hundreds of suspected cancer cases are not being investigated every week in Northern Ireland during the coronavirus crisis, it has emerged.
The number of red flag referrals is down by around 1,800 a week compared to a year ago.
A leading cancer expert said cancer referrals here must return to normal immediately to avert a "disaster".
Red flag is the term used to indicate a referral for a patient suspected of having cancer.
Last week it emerged there had been a 70% drop in red flag referrals, prompting calls for those with symptoms to seek help.
Figures obtained by the Belfast Telegraph from the Health and Social Care Board (HSCB) show the full extent of how the numbers have plummeted.
In January to February this year an average of 2,227 referrals a week were recorded, dropping to 1,000 by the week beginning March 16. This had dropped to 700 a week by last week.
For the first three weeks of this month alone 2,360 referrals - around 800 a week - were recorded. That compares to 7,704 in the first three weeks of April 2019, around 2,570 a week.
A red flag referral is not a confirmed cancer diagnosis. Most referrals do not turn out to be cancer.
However, experts have voiced alarm that many cases will be missed, and the long-term impact on the health system.
Professor Karol Sikora, the chief medical officer of Rutherford Health cancer treatment facilities, has previously worked as a Government medical adviser and headed the World Health Organisation's cancer programme between 1997 and 1999.
He said a "disaster" in cancer care across the UK can be averted, but only if the situation is addressed now.
"The pattern is caused by the fact that the hospitals are switched over to Covid and all routine diagnostics have stopped," he said.
"So all the cancer diagnostic pathways across the country have essentially been put on hold.
"With the realisation this has happened, the Government is now trying to get them all back into action. The problem will be it's like releasing a dam. Not everyone will be treated in a prompt way, and will take around three months to clear the backlog.
"So the longer we wait to do that, the worse it gets. It's the same problem everywhere. The operating rooms are standing idle, the surgeons are idle.
"Everyone is waiting to get going and I think we need to find ways to do that. It's not just cancer but things like cardiac services and heart operations."
Professor Sikora said the NHS had done "remarkably well" in dealing with Covid-19, but it had been at the expense of patients with other illnesses.
"Across the UK every year a total of 30,000 people are diagnosed with having cancer. I reckon for April the total will be less than 5,000.
"If we get going again in May, I think the outcome for most patients will be fine. But if we have to go six months like this it's going to be a disaster."
Colleen Shaw, the chief executive of Friends of the Cancer Centre in Northern Ireland, said the HSCB figures were "very concerning".
"It's understandable that Covid-19 has been a key health priority and we are extremely grateful to all those in our health service who have been working hard to help us through this crisis. However, cancer has not gone away," she said.
While recognising coronavirus will be a serious issue for some time, she said she hoped cancer screening, diagnosis and treatment will return to normal to prevent a future rise.
She added: "In the meantime, we know it's a very worrying time for everyone at the moment, but we would encourage anyone who is experiencing symptoms of cancer, or worried about any changes to their body, to contact their GP as soon as they can."
Margaret Carr from Cancer Research UK said people who are worried must come forward.
"If lots of suspected cancer cases are not investigated until a later date, there's a risk of breaking an already flooded NHS system," she said.
Red flag is the term used to speed up appointments when a family doctor feels there is a possibility that symptoms could indicate cancer. This ensures the patient will see a specialist as quickly as possible. Having a red flag referral does not necessarily mean someone is a confirmed case. Most people with a red flag referral do not have cancer.