A watch and act alert was also in place for people in the Pannawonica townsite in Ashburton Shire.
The new blaze came as more than 200 firefighters continued to battle a fire that ripped through dozens of tinder-dry, semi-rural properties near Perth, destroying 18 homes.
Previously at emergency level, the Perth blaze was reduced to a watch and act warning on Friday afternoon, although authorities warned it could take at least another three to four days to bring the fire, which has a 64km perimeter, under control.
Watch and act alerts remained in place for parts of Jandabup, Melaleuca, Wanneroo and Marginiup in the City of Wanneroo on Saturday.
Residents were being warned there was still a possible threat to lives and homes as the fire continued to burn and the weather forecast remained unpredictable, with a weekend of 39C temperatures.
Residents in parts of the lower west and southwest districts were told to prepare for severe storms throughout Saturday night.
“If you live in parts of Lower West and South West districts you should take action and stay safe with severe weather to come,” the Department of Fire and Emergency Services said.
“Locations which may be affected include Armadale, Harvey, Kalamunda, Midland and Pinjarra.”
Disaster recovery assistance - jointly funded by the federal and WA governments - would be made available to those affected by the Perth fire, Emergency Management Minister Murray Watt said on Saturday.
The funded assistance would go to individuals, families, primary producers and small businesses in the cities of Swan and Wanneroo.
The assistance would help meet essential needs such as emergency accommodation, food, clothing and personal effects, and personal or financial support services, Senator Watt said in a statement.
”This is an incredibly distressing time for those who have been forced to evacuate and are waiting to hear about the condition of their homes, and of course for those who have lost their homes,” he said.
“Interest rate subsidies will also be available for eligible small businesses and primary producers to repair or replace property damaged or destroyed by the bushfire.”
The federal and WA governments were also working together to support the cities of Swan and Wanneroo to cover the costs of counter-disaster operations and the repair of power lines and other essential public assets damaged by the fire.
WA Emergency Services Minister Stephen Dawson said the fire remained a major incident and was not contained.
“We will have hot weather over the next few days and so we’re not out of the woods just yet,” he told reporters as he fronted media with Premier Roger Cook on Friday afternoon.
The blaze started in a pine forest on Wednesday and forced hundreds of people to flee their homes as strong winds fanned embers a kilometre ahead of the fire front.