Only seven ambulances were free to respond to emergencies across the whole of Sydney for more than an hour on Tuesday afternoon, after paramedics were left stranded at hospitals that were too full to admit their patients.

NSW Ambulance senior managers had to leave their desk jobs and step in as paramedics from about 2.30pm to cope with demand after an increased number of triple-0 calls and long waiting times at emergency departments.

Ambulances wait at Liverpool Hospital after transporting patients on Tuesday.

Fairfax Media understands there were 13 outstanding jobs around Sydney just after lunchtime on Tuesday to which ambulances could not attend, four of which were time-critical medical transports.

Two ambulances were forced to wait nearly two hours before they could discharge their patients at Liverpool Hospital while two more were stuck at St Vincent's for an hour.