A patient at Sydney's Westmead Hospital has described spending almost an entire day waiting in the emergency department before leaving without receiving a hospital bed.

The patient, identified by his first name Adnaan, went to Westmead Hospital in late August after experiencing severe abdominal pain and shortness of breath. He said his symptoms became serious enough that he left work and sought emergency medical attention.

According to his account, he arrived at the emergency department at about 5pm. He described the department as extremely crowded, saying that seats were occupied and that some people were standing or sitting on the floor.

Adnaan said he remained at the hospital for approximately 23 hours, waiting on a hard chair while staff dealt with the large number of patients.

He was eventually told that there were no available beds and that admission would require further waiting. Adnaan said hospital staff told him there were only three doctors available for 144 patients at the time.

Despite being advised that he had a slightly ruptured kidney, he ultimately decided to leave the hospital against medical advice after waiting through the night and into the following afternoon.

The case comes as new health figures show significant pressure on emergency departments at Westmead Hospital. According to the figures reported by the ABC, only 49.1 per cent of patients at Westmead began treatment within the recommended timeframe.

The hospital's average emergency department wait was reported at six hours and 30 minutes, compared with a NSW-wide average of three hours and 49 minutes.

The figures also showed that the median time for patients who needed admission or transfer was 16 hours and 35 minutes. This represented an increase compared with the previous year.

Westmead Hospital is one of the major hospitals serving western Sydney and is part of the Western Sydney Local Health District. Its emergency department manages large numbers of patients from across the region.

The situation illustrates the difference between emergency department arrival and the time required for a patient to receive treatment, assessment, admission or transfer. Hospitals can experience pressure when large numbers of patients require care at the same time while inpatient beds and medical staff are limited.

Adnaan's experience is being reported alongside broader data about emergency department performance rather than as evidence that every patient experiences the same wait.

The latest figures and patient account have renewed attention on emergency department capacity and hospital access in western Sydney. The available report also documents the difficulties experienced by patients when emergency departments become heavily overcrowded.