Scotland's newest hospital has apologised after A&E waiting time performance fell to a new low.
Last week only 77.2% of patients at the Queen Elizabeth University Hospital (QEUH) in Glasgow were dealt with within four hours.
A total of 386 patients waited for longer, with 29 of them in A&E for more than eight hours.
The government target is for 95% to be seen and either admitted, transferred or discharged within four hours.
The £842m facility, formerly known as the South Glasgow University Hospital, started taking patients in April.
Dubbed a "super-hospital", the campus replaced the Royal Hospital for Sick Kids at Yorkhill, the Southern General Hospital, the Western and Victoria infirmaries and the Mansionhouse Unit.
In June, the Scottish government announced that a team of experts would be sent in to help staff improve A&E waiting times at the site.
Performance rose markedly as a result, with the hospital hitting a rate of more than 90% since the end of July.
But in the week ending 4 October, the figure dropped sharply, making it the worst performing site in Scotland.
Hospital director Anne Harkness said: "Our emergency department and immediate assessment unit were both extremely busy last week and we apologise to those patients who had a long wait to be admitted.
"After a number of weeks where the A&E performance at the Queen Elizabeth University Hospital had shown a sustained improvement, these latest A&E figures are particularly disappointing.
"Our analysis for this most recent performance has shown that the new model of care within our immediate assessment unit has been seeing significantly more patients than was projected.
"Elsewhere, patients are also spending longer in hospital than we had anticipated.
"We are fully committed to tackling these issues and are putting in place a number of immediate steps to improve the situation."
Health Secretary Shona Robison said demand for services at the new hospital had been higher than anticipated.
She said: "It is clear that improvements are needed at QEUH to further increase capacity and drive down waiting times - patients should expect nothing less.
"The opening of the QEUH involved moving three existing hospitals on to one site and was one of the biggest and most complex of its kind in Europe.
"I have spoken directly with the chairman of NHS Greater Glasgow and Clyde and have received assurances from the health board that immediate action is being taken to create more capacity in the immediate assessment unit in order to improve the flow of patients, as well as working with staff to streamline clinical processes to support early discharge."
Dr Richard Simpson, Labour's public services spokesman, said: "This is an absolutely shocking state of affairs. For Scotland's flagship hospital to need specialist support twice in just four months is utterly incredible.
"It now seems that the handling of the transfer of patients has been completely botched.
"I asked SNP Health Minister Shona Robison back in May to consider pausing the transfer of patients to ease the burden on the new hospital and she said no.
"This is a problem made by the poor decisions of the SNP government, like squeezing health spending in Scotland harder than even the Tories in England."
The latest performance figures show that across Scotland, 94% of patients were seen within four hours, down from 95% the week before.
A total of 109 people had to wait eight hours or more to be treated while no patients waited 12 hours or more.