Hospitals have struggled to meet the four-hour treatment time in accident and emergency departments for the first time since April as winter pressures start to bite.
Last week, 94.8% of NHS patients in England were treated within the target time of four hours.
It is the first time that emergency departments, including minor injuries units and urgent care centres, have missed the 95% target since April, NHS England figures show.
Waiting times were worst in major A&E wards where just 92.2% of patients were seen within four hours.
Across England, 3,678 patients were forced to wait between four and 12 hours for treatment.
And five patients were not seen for more than 12 hours, the figures show.
Last week, hospitals treated more than 415,000 patients in A&E - 3,500 patients more than the previous week.
Dame Barbara Hakin, chief operating officer for NHS England, said: "It is of course disappointing that any patient has to wait longer than they should in A&E; however, we are now seeing many more patients than ever before.
"Last week was the busiest so far this year, with 415,400 attendances and 105,800 emergency admissions - the highest number of emergency admissions since we started collecting data in November 2010.
"We know the A&E standard is ambitious and that is only right. This is the first week since April the 95% standard has not been met; however, we do know that sometimes this will happen. Every year we see a dip in the figures for December, with week-on-week variations, which is why we fully assess how local systems are coping with winter pressures over a longer period.
"We knew this winter would be difficult but it is important to stress the NHS continues to deliver a good service, with 94.8% of people going to hospital for urgent care this week treated, admitted or discharged within four hours. This is thanks to the hard work and dedication of our frontline staff."