Emergency departments at four Sydney hospitals have recorded significant blow-outs in the proportion of patients waiting too long to be treated.

More than 60 per cent of patients who presented at Westmead Hospital's emergency department were not treated within the clinically recommended timeframe in April to June this year, found the Bureau of Health Information's latest quarterly report.

NSW hospital emergency departments are recording rising numbers of presentations. Credit:Damian Shaw

The results meant the majority of people who came through the hospital's ED did not have their treatment start on time compared to just under 46 per cent over the same period in 2016.

The 14 percentage point drop in on-time treatment – the biggest decrease of any NSW hospital – was almost matched by Blacktown Hospital, where 53.8 per cent of ED patients did not start their treatment on time, down 13.6 percentage points on the same quarter last year.