Just 71.5 per cent of people visiting A&E in the week to September 12 were seen within four hours, a drop from the figure of 74.6 per cent the week before.
The Scottish Government target is 95 per cent.
It is the fifth time in six weeks that the figure has set a new record low, after it fell to 76.5 per cent in the week to August 1.
It comes amid growing pressure across the NHS, with high demand and staffing shortages often blamed for the increasing issues.
And figures obtained by the Scotsman revealed a 20-fold increase in the number of people waiting more than 12 hours for an ambulance in 2020/21 compared to the previous year.
The Scottish Government has asked the Army to step in to support ambulances, which are facing long waits to drop patients off at over-stretched A&E departments.
Health Secretary Humza Yousaf is expected to update parliament on this request on Tuesday.
Liberal Democrat leader Alex Cole-Hamilton said Mr Yousaf must “answer for his job” over the growing crisis.
"This crisis is years in the making,” he said.
“The Health Secretary had been warned that emergency care was crumbling, and yet after a month of record breaking waiting times things still aren’t improving.
“The pressure in the ambulance service and in A&E departments is deeply intertwined, and so as the Health Secretary comes to parliament today he must answer for his job and offer an apology to patients, families and staff.
“Something seismic needs to be offered to turn this around.”
Scottish Conservative Shadow Public Health Minister Sue Webber said: “Week after week, Humza Yousaf has completely failed to get on top of this situation, and it is patients who are paying the price.
“The response to this crisis has been pitiful.”
Labour's Jackie Baillie said: “The crisis in our NHS is spiralling further and further out of control.
“Lives are now being jeopardised on a daily basis due to the failure of this SNP government to support the NHS.”
Some 1,895 people out of the 27,354 who went to emergency departments in Scotland in the week of September 12 – 6.9 per cent – waited more than eight hours to be seen.
A further 551 (two per cent) waited more than 12 hours.
A spokesperson for the Scottish Government said: “Our NHS staff have faced unprecedented pressures over recent weeks as they work tirelessly and consistently to respond to the pandemic whilst continuing to provide vital treatment and optimal patient care.
“We are in daily contact with every board and are monitoring the situation closely. As part of the NHS recovery plan we have committed £27 million towards the redesign of urgent care to ensure people receive the right care, at the right place and avoid unnecessary hospital attendance.”
She added: “We are working closely with those sites facing the greatest challenges to ensure rapid recovery plans are in place and are in contact daily.”