The NHS is to scrap the requirement to see A&E patients within four hours in pilot areas over the next few months.
Hospitals will prioritise mentally ill patients as well as patients with suspected heart attacks, sepsis , stroke and severe asthma attacks.
They will also introduce a fast track target to see people who arrive at A&E with a mental health crisis within one hour.
Other patients with more minor injuries face even longer waits.
Theresa May told the NHS to review waiting targets last June after hospitals have failed to hit the A&E benchmark target – to see 95% of patients within four hours – since July 2015.
The NHS is not identifying which areas which will be piloting the scheme to prioritise more serious patients and measure average waiting times. It would see patients with minor injuries not admitted.
Prof Andrew Goddard, president of the Royal College of Physicians, said: “Over the last two decades the existing targets have played a crucial part in driving dramatic improvements in waiting times for patients.
“It is important that any changes build on these achievements. At present the waiting list for planned treatment including surgery continues to grow and altering targets will not alone solve the underlying challenges we face.”
Figures for January showed that A&E waiting times in England reached their worst level since records began.
Just 84.4% of patients were treated or admitted in four hours, against a 95% target, meaning nearly 330,000 patients waited longer than they should.
The data also showed that 83,519 people in January endured very long waits – often called trolley waits – to be admitted to hospital.
This data will not be published in the future but is likely be rolled into a measure of the average time people spend in A&E.
Under the plans, patients will receive an assessment by a medical professional when they walk through the door of A&E, and cases will then be prioritised according to the level of urgency.
After the review is completed the four-hour target could be scrapped nationwide from April 2020.
NHS England stresses the measures are still proposals and implementation will be subject to the outcome of the trials.
Changes to other waiting targets will also be trialled between now and April 2020 after a collapse in standards.
The current 18-week target for people to start treatment could also be replaced by one measuring the average time taken to start treatment.
Nuffield Trust chief executive Nigel Edwards said: “Given the history of targets having unintended consequences we will need to watch closely as these trials go ahead.
“There is a risk that getting rid of the 18 week limit on waits for planned procedures could mean the proportion of people going without care for an unacceptably long time drifts upwards.
“And we need to be hard-headed about how much difference fine tuning targets will make – the root causes of poor performance lie in a lack of staff and capacity, which we have barely started solving.”
Currently suspected cancer patients should have an appointment with a specialist within two weeks. The new standard being piloted would see time from GP referral to diagnosis or cancer being ruled out take no longer than 28 days.
Baroness Delyth Morgan, chief executive at Breast Cancer Now, said: “The current ‘two-week wait’ for breast cancer has been hugely successful in transforming the experiences of people referred to a specialist to investigate their symptoms.
“With these proposals representing a shift to instead give reassurance of a 28-day wait for diagnosis, it’s vital we ensure they will further improve patient experience and build on years of progress.”
A target to discharge, admit or transfer 98% of patients arriving in A&E within four hours was introduced by the Labour government in 2004. It was then downgraded to 95% in 2010.
NHS boss Simon Stevens has already indicated he wants to scrap the four-hour A&E target.
NHS England said around a fifth of all emergency admissions from A&E happen in the final 10 minutes before the deadline, suggesting hospitals are trying to game the figures.
Prof Stephen Powis, the NHS in England’s national medical director, said: “The NHS is aiming to improve care for patients and save hundreds of thousands more lives over the coming years, with greater access to mental health support, better treatment for the major killer conditions and services which are more joined-up, personalised and closer to home.
“So, as we build an NHS that is fit for the future, now is the right time to look again at the old targets which have such a big influence on how care is delivered.”