Official statistics also show that the proportion left waiting more than eight and 12 hours in December were at the worst level for a single month since records began in 2007.
Scottish Conservatives health spokesman Miles Briggs described the figures as “an utter disaster”.
Of the 141,416 people admitted to A&E in Scotland during December, just 83.8 per cent were treated, transferred or discharged within the target time, leaving almost 23,000 patients waiting over four hours.
The figure is 1.3 percentage points below the previous low in December 2017 and a long way short of the Scottish Government’s “national standard” of 95 per cent, which was last met in August 2017.
NHS Scotland statistics also reveal 3,899 (2.9 per cent) of patients spent more than eight hours in an A&E department, while 1,107 (0.8 per cent) patients waited more than 12 hours.
Mr Briggs said: “The SNP has caused this crisis by cutting beds and failing to support primary care. Patients are waiting in pain, discomfort and distress which in turn significantly affects staff.
“The SNP has had 13 years to improve our NHS for patients and staff and this is the result – rock bottom performance across the board.”
He added: “Our Scottish NHS is falling apart and the SNP is arguing over flags and lighting up buildings in Europe.
“The people of Scotland deserve better, they deserve a Scottish Government that cares about them.”
NHS Lanarkshire was Scotland’s worst-performing health board for A&E waiting times with 77.2 per cent of patients seen within four hours, followed by NHS Greater Glasgow and Clyde on 79.9 per cent.
There were three NHS boards that exceeded the 95 per cent target – Orkney (97.5 per cent), Tayside (96.7 per cent) and the Western Isles (96.3 per cent).
The target of 95 per cent of patients being seen within four hours was introduced in 2007 and described as “a milestone towards returning to the 98 per cent standard”.
Scottish Liberal Democrat health spokesman Alex Cole-Hamilton MSP said: “The SNP health secretary said that she would turn round years of decline but these figures confirm that she has spectacularly failed.
“We can only have a health service that delivers for patients and staff if we are prepared to put in the resources to make that happen.
“Liberal Democrats have consistently asked for new mental health practitioners in every A&E, available 24/7, to alleviate the pressure on staff and get people the treatment they need quickly.
“It is time the Scottish Government delivered and it should take this opportunity in the budget later this week.”
Health secretary Jeane Freeman said: “In December 2019, our core A&E departments saw the highest level of attendances for that month ever.
“This was in part due to the early onset of the flu season and an increase in respiratory conditions.
“However, Scotland’s core A&E departments continue to be the best performing in the UK.
“In December, Scotland’s core A&Es were almost 13 percentage points better than their counterparts in England and were over 15 percentage points better than those in Wales.”
She added: “We’re investing nearly £20 million to support improvements in unscheduled care to help address the challenges our A&Es face.
“That includes £13.4 million to ensure quality of care, patient safety and access to services are maintained over the winter period. We’re very clear that providing effective out-of-hours care to ensure non-emergency patients don’t need to go to A&E is integral to tackling waiting times – that’s why we continue to support the delivery and redesign of GP-led out-of-hours services in line with Sir Lewis Ritchie’s report.”
Meanwhile, the number of patients forced to stay in hospital when they are medically well enough to leave has risen by 12 per cent in a year. A hospital census carried out in December revealed 1,379 people had their discharge delayed, including 400 who had been waiting six weeks or more. While the overall number was the lowest monthly total since April 2019, it was up from the 1,236 recorded in the December 2018 census.
Age Scotland’s head of policy, Adam Stachura, said: “It is once again extremely disappointing to see how many older people are being kept in hospital because of the failure to get to grips with the lack of available social care in the community.”