In the event of an emergency, the first thing a person does is ring triple zero and the voice on the other end of the line renders assistance and sends out help.

But, on Monday a number of people who rang triple zero for an ambulance found they were left without help.

A number of people who called for an ambulance on Monday were left waiting. Credit:Damian Baker

Fairfax Media understands there were more than 30 outstanding triple zero jobs on Monday morning and more than 10 that were time-critical medicals.

At one stage, only three ambulances were available to cover Sydney for a brief time and some paramedics were asked to work overtime.