There were two million attendances at A&E departments in England in September, with 88.9% of patients being seen within the target of four hours, the latest figures show.
Performance statistics released by NHS England show 153 patients had to wait more than 12 hours from the decision to admit them to admission last month.
In all, a total of 44,312 patients were forced to wait longer than the four-hour target - the highest figure since April.
Health leaders have been warning as winter approaches, the NHS is likely to come under immense strain once again although this year it has had little respite during a very busy summer.
Tom Sandford, director of the Royal College of Nursing England, said: "These figures sound the alarm bells for the NHS as we head towards winter.
"Admissions are up on last year and the four hour target has been missed every month since July 2015.
"The lack of enough nursing staff to provide safe and effective care feeds into these systemic issues threatening to bring our health care system grinding to a halt as the cold weather sets in.
"Budget day is approaching and the £20 billion promised to the NHS can't come soon enough.
"The Government must produce a fully funded workforce plan, underpinned by legislation, that responds to population need and prioritises nurse recruitment and retention."
NHS Providers deputy chief executive, Saffron Cordery, said: "These figures reflect once again the steep and relentless rise in the demand for care that trusts are facing, and the fact that this has become a year-round phenomenon.
"They also highlight the frustrating paradox of trusts and frontline staff pulling out all the stops to cope with growing pressures, but slipping further and further from the constitutional standards the public have been told to expect, and the recovery trajectory set out in NHS planning guidance.
"Waiting lists for operations continue to grow, but inevitably, attention will focus on performance in A&E where - compared with the previous September - the number of people coming in for help rose by over 4% to more than two million.
"Alongside increased attendances we are seeing a growing proportion of patients having to be admitted as an emergency. The total has risen by nearly 5% in the last 12 months.
"Yet again, NHS trusts have responded to the challenge."
She added the number of people admitted, transferred or discharged within four hours also increased by more than 3% compared with the same time last year.
Dr Nick Scriven, president of the Society for Acute Medicine, also called for better planning and investment.
He said: "The relentless pressure seen throughout the year is an indication of what is in store this winter.
"The sporadic funding announcements we've seen will serve only to help trusts maintain stretched services, not improve capacity and resource to the level it is required.
"That requires long-term planning and investment throughout the NHS and social care and a desire to focus on effective systems and processes as opposed to patchy cash injections which fall well short of the level required to oversee real change."