The latest figures for the week ending December 3 show that 89.7 per cent of patients were seen and either admitted, transferred or discharged within four hours, below the Scottish Government’s 95 per cent target.
The figure is the worst since the 87.9 per cent recorded in the week ending January 8.
A total of 292 patients spent more than eight hours in an emergency department while 59 waited for more than 12 hours.
Scottish Liberal Democrat health spokesman Alex Cole-Hamilton MSP said: “Winter is well and truly here and we are already seeing the worst A&E performance since the New Year.
“Despite the hard work of NHS staff, too many patients are waiting too long for treatment. We cannot afford to let this slip further backwards.
“Scottish Government ministers need to ensure that under pressure A&E staff have the support and resources they need to be able to meet demand, especially over the winter period, and deliver the best care for patients.”
The Scottish Government said winter plans were in place and highlighted a rise in flu and norovirus cases in recent weeks, leading to increased pressure or the closure of hospital wards.
Health Secretary Shona Robison said: “We are beginning to see a rise in seasonal illnesses across the country which is why we’ve taken steps to ensure boards have robust winter plans in place to build resilience across the whole system.
“It is not unusual for A&E waiting times to fluctuate from week to week and from site to site across winter, due to norovirus, flu and respiratory-like illnesses or an increase in slips and trips.
“I’d like to pay tribute to the hard work of all NHS staff across such a busy period for all the work they are doing to ensure patients receive high quality care and treatment.
“Scotland’s core A&Es have outperformed those in the rest of the UK for more than two and a half years. We have put record investment into the NHS this year, with increased levels of staffing and an extra £22.4 million for unscheduled care throughout the year and robust winter planning.”