NHS hospitals in England were close to capacity in the first week of December, with 94.2% of beds across the country occupied, close to last winter's peak of more than 95%.
Bed capacity is a key indicator of how the hospital system is coping with increased winter demand, and the high level of bed occupancy so early in the season will add to concerns that this winter may be just as pressured as last year.
The figures will be particularly alarming as the weather has thus far been relatively mild and there is no sign of a flu outbreak on the scale that caused such difficulty for the system a year ago.
NHS England says bed occupancy should not exceed 92% while health experts including the Royal College of Emergency Medicine say anything above 85% can compromise patient safety.
The bed occupancy figures were contained in the first weekly winter situation report from NHS England, which tracks demand at hospital trusts across the country.
The figures also showed that 10,700 ambulances, more than 11%, experienced delays of more than 30 minutes in completing the handover of patients at hospital. Almost 2,000 of these were delays of more than an hour.
Monthly statistics for A&E performance in November showed a decline against the same period last year.
Just over two million patients attended A&E during the month, with 87.6% treated, admitted or discharged within four hours, down 1.2% on the same month last year and well short of the target of 95%, which has not been hit nationally for more than three years.
NHS England said that because of the increase in attendances more patients were being seen within four hours, but acknowledged demand was placing the system under strain.
"NHS staff continue to work hard to deal with increased demand across the board, seeing 1,000 more people within four hours in A&E every day in November compared to last year.
"A growing proportion of people are getting same day emergency care which prevents the need for an overnight stay and hospitals have freed up an additional 742 beds, by working closely with councils to help more people return home with the right care in place."
Labour's shadow health secretary Jonathan Ashworth said the figures were "hugely concerning".
"Winter is only just beginning for our NHS and these are hugely concerning figures that don't bode well for the difficult weeks ahead.
More from NHS
"While government remains paralysed by Brexit infighting, the NHS is struggling as a result of years of underfunding, cuts and staffing shortages. Rather than their self-interest, Tory ministers must start prioritising patients' interests by outlining proposals for the NHS this winter.
"It would be totally unforgivable if patients suffered another winter crisis like the ones we've seen in recent years."