Almost 30 per cent of patients are waiting too long for treatment across NSW's emergency departments as the number of people presenting to the state's hospital rises.

At one Sydney hospital, about 324 patients over a three-month period had to wait almost an hour for treatment that should have been started within 10 minutes.

More than three-quarters of a million people went to emergency between April and June. Credit:Edwina Pickles

The unprecedented increase in emergency department patients has put pressure on hospitals not designed to cope with such numbers, the Australian Medical Association NSW said.

More than three-quarters of a million patients (754,442) presented to emergency in April to June, the latest Bureau of Health Information report shows. That's up 8.2 per cent on the same quarter last year, and it takes the number of patients who have gone through emergency to more than 1.5 million.