Emergency services on Tuesday afternoon warned people in and near the park they should leave the area immediately or be prepared to defend their homes.
Late on Tuesday night (AWST) the Department of Fire and Emergency Services (DFES) said a watch and act warning had been downgraded to a bushfire advice as the blaze was controlled
WA Police were advised of multiple fires in the park about 2.50pm (AWST) on Tuesday and are treating them as suspicious, with the arson squad investigating.
"Early indications suggest there are multiple ignition points," a police statement said
Police urged anyone with information on the fire to come forward and said rewards of up to $25,000 were available for intelligence that leads to a conviction.
The majority of the park has been reopened to the public.
It's the second bushfire in Perth's inner suburbs this week, with firefighters on Monday called to a blaze in Bold Park, which is also largely bushland and is 437ha in size.
Kings Park is one of the world's largest inner city parks and is about 400ha in size and 10km around.
It is a mixture of bushland, botanic gardens and grassed parklands.
The park is also home to the State War Memorial and is surrounded by hospitals, apartment buildings, family homes, busy inner-city roads and office buildings.
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