The percentage of patients seen in Scottish accident and emergency departments within a four-hour period has fallen to the lowest level on record.
Official statistics also show 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”.
However, the health secretary said that despite the figures, Scotland still had the best-performing emergency departments in the UK, and partly blamed the “early onset of the flu season” for the decline.
Of the 141,416 people admitted to A&E in Scotland during December, just 83.8% were treated, transferred or discharged within the target time, leaving almost 23,000 patients waiting more than four hours.
The figure is 1.3% below the previous low in December 2017 and well short of the Scottish Government’s “national standard” of 95%, which was last met in August 2017.
NHS Scotland statistics also reveal 3899 (2.9%) of patients spent more than eight hours in an A&E department, while 1107 (0.8%) patients waited more than 12 hours.
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.”
Health secretary Jeane Freeman said December had seen the highest ever number of patients attend Scotland’s A&Es.
She continued: “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% better than their counterpart in England and were over 15% better than those in Wales.”
NHS Lanarkshire was Scotland’s worst-performing health board for A&E waiting times with just 77.2% of patients seen within four hours, followed by NHS Greater Glasgow and Clyde on 79.9%.
There were three NHS boards that exceeded the 95% target – Orkney (97.5%), Tayside (96.7%) and the Western Isles (96.3%).
The target of 95% of patients being seen within four hours was introduced in 2007 and described as “a milestone towards returning to the 98% standard”.
Scottish Liberal Democrat health spokesman Alex Cole-Hamilton said: “The SNP health secretary said that she would turn round years of decline but these figures confirm that she has spectacularly failed.”