The chief executive of Belfast Chamber of Trade, Mr Frank Caddy, has said the freezing weather in the North is having disastrous consequences for post-Christmas sales shopping in the city centre.
More snow was predicted overnight, and driving conditions remain treacherous with thick, freezing fog compounding the problems caused by compressed snow and ice.
Disruption of transport remains widespread as buses, trains and airlines struggle to cope with the extreme conditions. Post-Christmas sales are understood to be down by up to 50 per cent on last year.
The massive slump has been caused by the early closing of shops and a lack of customers in Belfast city centre.
There were fears that as subzero temperatures appeared set to continue over the next few days, weekend shopping would also be affected.
Mr Caddy said: "Transport has been practically killed in Belfast because of the snow. I would say there has been as much as a 50 per cent fall-off in sales from the same time last year."
On Thursday night temperatures in the North fell as low as minus 13 degrees. In Belfast temperatures plummeted to almost minus 10 degrees. The lowest-ever recorded temperature in the city is minus 11 degrees. Hospitals in the North have reported a dramatic rise in the number of broken bones. The Ulster Hospital in Dundonald said it had dealt with 22 fractures in 24 hours, twice the normal number.
"Elderly people seem to have the sense to stay in, but we have been surprised at the number of young people coming in with injuries," a spokeswoman said. Dr Ian Gordon, a GP in the northwest, expressed dismay at the response from the Road Service to the weather conditions.
"We provide a 24-hour, seven-day service right through the holidays, and I do think we have a right to expect that the roads are at least made as safe as possible for us," he said.
"Obviously we can't expect all the minor roads to be cleared, but I do think a lot more effort should have been put in," Dr Gordon added.
However, the Eastern Division's network maintenance manager of road services, Dr Andrew Murray, insisted everything possible was being done.
"We only salt 27 per cent of the road network in Northern Ireland so there are a lot of minor roads that we haven't been able to touch yet," he said.
"And the effectiveness of salt reduces very markedly at temperatures below minus 5, and we have had temperatures below minus 10. At those temperatures salt really doesn't have a great effect," Dr Murray said.
Translink said its trains and buses were subject to delay. Cross-Border bus services from Derry were cancelled. The North's airports remained open but flights from Belfast International Airport to Liverpool, Birmingham, Edinburgh and Glasgow were delayed.
The Northern Ireland Prison Service said visits to Maghaberry jail and Hydebank Young Offenders' Centre were cancelled. Belfast New Year's Eve outdoor celebrations may be moved indoors if the freezing weather continues until Sunday.