NHS England urgent and emergency care director Prof Julian Redhead said alongside the high number of flu cases in hospital the NHS was having to plan for more doctor strikes in the lead up to Christmas.
British Medical Association members are taking part in a five-day walkout from 17 December in their long-running pay dispute.
Prof Redhead said: "Today's numbers confirm our deepest concerns - the health service is bracing for an unprecedented flu wave this winter. Cases are incredibly high for this time of year and there is no peak in sight yet."
He said staff could be stretched "close to breaking point" in the coming weeks.
Already close to 2% of beds are occupied by flu patients, with the 1,700 average last week the highest at this point of winter since records began in 2010.
And at an NHS England board meeting on Thursday morning chief executive Sir Jim Mackey warned the numbers were continuing to rise sharply.
"We've had a really, really big increase," he said.
He suggested by the end of next week there could be anywhere between 5,000 and 8,000 beds occupied by flu patients. The highest level ever recorded so far is 5,400.
He said with this in mind the forthcoming doctor strike felt "cruel" and "calculated" and aimed at "causing mayhem".
Prof Redhead said because of the demands being place on the NHS it was vital patients used services sensibly.
NHS England published A&E attendance figures showing between 1 November 2024 and 28 February 2025 there were:
The attendances were to either major A&E units or minor injury units run by hospitals.
Although research shows one of the factors driving unnecessary A&E visits is difficulty accessing GP services, with latest figures showing more than a fifth of patients cannot get through to their GP on the day they try.
NHS England said patients can get prescription-only medication – traditionally dispensed by GPs – at pharmacies for a range of common conditions, including a sore throat, sinusitis and earache.