The figure has been declining since the summer amid high demand, staffing shortages and a lack of patient flow through hospitals.
In the week to October 3, just 71.3 per cent of patients were seen within four hours, a five percentage point drop on the previous week, according to a data published by Public Health Scotland.
The figure is the lowest since records began in 2015, with the Scottish Government target set at 95 per cent.
With 25,000 visits to A&E in that week, it means more than 7,000 patients waited longer than four hours. Some 1,782 people waited more than eight hours, while a record 591 patients waited longer than 12 hours.
Last week, Scotland’s Health Secretary, Humza Yousaf, warned that Scotland’s NHS faces an “incredibly difficult winter” despite announcing a £300 million funding boost.
But opposition parties have now accused him of “overseeing a scandalous situation” and leaving A&E departments “beyond breaking point”.
Scottish Conservative health spokesman Dr Sandesh Gulhane said: “These figures are nothing short of an unmitigated disaster for Humza Yousaf.
“He has completely failed to resource our A&E departments that are beyond breaking point.
“Humza Yousaf is overseeing a scandalous situation in our NHS. Thousands of patients are not being seen within the SNP’s own target waiting times. His inaction is putting heroic staff under immense pressure before we even hit the peak winter period.
“The support being offered by our UK armed forces is incredibly welcome, but the Health Secretary has still not outlined a plan to maximise their use.
“His winter plan, which finally arrived last week, was far too little, too late. Humza Yousaf must finally show some leadership and get on top of this A&E crisis, which is now completely out of control.”
Scotland’s worst-performing health board once again was NHS Forth Valley, where 50.3 per cent of A&E patients were seen within the target time, followed by NHS Lanarkshire (62.9 per cent) and NHS Fife (64.8 per cent).
Only Scotland’s island health boards – NHS Western Isles, NHS Shetland and NHS Orkney – met the waiting time target.
Scottish Liberal Democrat leader Alex Cole-Hamilton said: “These numbers are terrifying for staff and patients alike.
“The NHS has always been a safety net for anyone who needs it but, after years of poor workforce management, that net has huge holes in it. Undoubtedly, people will be slipping through.
“The health service isn’t just struggling, it is being crippled by government mismanagement.
“There simply aren’t enough nurses available to prop hospitals up. There are thousands of vacancies, and the Health Secretary proposes recruiting just 200 from overseas.
“Those working through this are swamped, and have little reason to trust that this Government will make things better.
“The SNP have been in charge of our health service for 14 years. This crisis is entirely of their making. There is nobody else to blame.
“The Health Secretary needs to find a way to get more boots on the ground, and every single NHS staffer needs to be given a reason to stay. Things are going to get much worse before they get better.”
Scottish Labour’s health spokeswoman, Jackie Baillie, added: “It is becoming clear that we are on track for another winter catastrophe this year if we fail to act.
“The SNP need to listen to the warnings from staff on the front line and get a grip on the growing emergency in our NHS before the cold weather really bites.
“There is no time to waste when this many lives are on the line.”
Dr John Thomson, vice president of the Royal College of Emergency Medicine in Scotland, said he expects waiting time performances to get worse as winter progresses.
Speaking before the publication of new figures on Tuesday, he said: “The last four months have seen deteriorating four hour standard performance, and what that equates to is patients spending much longer than is necessary in emergency departments.
“That's particularly patients who are waiting for a bed elsewhere in the system, and they're spending much longer than ever before in emergency departments.
“They are continuing to receive the best quality care that we can give them… but the care they should be receiving is inpatient care within a speciality area, and that's not going to be the same.”
A Scottish Government spokeswoman said the coronavirus pandemic “has inevitably affected A&E attendance” and stressed that an additional £27 million had been allocated to redesign urgent care in the health service.
“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,” she said.
“To minimise pressures as much as possible this winter, we’ve recently announced £300 million of measures to help increase NHS and social care capacity in our hospitals and reduce delayed discharges.
“In the meantime, we will continue to work closely with those sites facing the greatest challenges to ensure rapid recovery plans are in place and are in contact daily.”