The Boeing 737 tanker flew to Perth from NSW overnight to assist as forests near the north Perth suburb of Yanchep burn.
Firefighters warn the blaze could continue for more than a week, having already burned through nearly 12,000 hectares of bush since sparking on Wednesday.
The fire has also destroyed at least one house and a petrol station, but firefighters have saved over 6,000 homes according to the WA Department of Fire and Emergency Services.
Heatwave conditions are not helping.
Tops of 40 degrees are predicted for Perth on Sunday, as well as wind gusts up to 45km/h.
Around 400 career and volunteer firefighters are battling the Yanchep blaze and conducted backburning overnight in an effort to stop it spreading further.
SES volunteers are also attending.
A total fire ban remains in place in Perth.
In NSW, the massive Gospers Mountain bushfire that has been burning in Wollemi National Park for over a month now, continues.
NSW Rural Fire Service said that fire is being contained.
The fire has now burned through over 367,000 hectares after merging with several others.