Police are searching for Lachlan Bowles, 25, in Kellerberrin and the surrounding districts, where members of the public have been warned to remain indoors.
"The man is believed to be travelling on foot around Mission Road, in the Kellerberrin and Bencubbin areas," a WA police spokesman said on Thursday.
"He is believed to be armed and dressed in camouflage clothing."
A man is understood to have been fatally shot at the grain silo in Kellerberrin, about 200 kilometres east of Perth, about 8.40am.
Police issued an active shooter alert and warned media to stay away from the area, saying it was unsafe.
Annamaria Lucente, manager at Kellerberrin Hotel Motel, said the close-knit town of about 950 people had been told to stay indoors.
'The whole town is in shock," she told AAP.
The gunman fled the grain silo site in a vehicle after the incident, with police initially saying one person had been injured and transported to hospital.
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