Fires burning across Western Australia have impacted tens of thousands of hectares of land as reinforcements arrive from New South Wales.

A large air tanker and 36 firefighters landed in WA today to help bring the bushfires under control.

"The weather conditions will be milder today but I want to emphasise that there is still a real threat to lives and to communities and to homes," WA emergency services minister Stephen Dawson said.

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There are a number of fires in the state, but the two largest are in Denmark, in the state's south and in Bridgetown, closer to Perth.

"The incidents combined have impacted more than 60,000 hectares and currently, we have more than 1,000 personnel in attendance combatting or managing the fires," Mr Dawson said.

"I've been in a couple, but this is by far the scariest… it's gotten so close to the houses," farmer Sam Pearce, who lives in Denmark, said.

"It's relentless because the wind would change… it's almost like it was determined to burn everything there," Geoff Dowling, also a farmer, said.

A home and a shed were destroyed in Bridgetown, as well as a number of sheds at the waste facility and transfer station.

In nearby Hester, a timber treating plant has been mostly destroyed and authorities are concerned about the ash and dust blowing around, and potentially contaminating water sources.

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People have been evacuated while authorities assess the extent of the damage and determine how dangerous the ash is.

Four houses have been lost in Denmark since the blaze began.

Temperatures have dropped today but the weather is forecast to heat up again towards the end of the week.

Firefighters are hoping to get the blazes under control before then, given the Denmark fire doubled in size on Friday night in hot conditions.

Conditions are constantly changing – the best place for up-to-date information is the Emergency WA website or the Department of Fire and Emergency Services Twitter.