Five fires in one hour in Sydney's west

An arsonist is on the run after starting five fires in an hour in Sydney's west, with one leaving an elderly woman needing medical assistance.

Emergency services were called to Bankstown just after 3am on Friday, after reports of several fires.

The five fires were lit within the hour and were believed to be linked, police say.

A fire in Marion Street resulted in an 84-year-old woman being treated for smoke inhalation after the back of her home was set alight.

All the fires are being treated as suspicious.