Racing at Northam Racecourse was abandoned on Thursday afternoon after a barrier attendant was reportedly struck by lightning on the track.
The man, aged 57, was airlifted to Royal Perth Hospital overnight and remained in a critical condition Friday morning.
It is understood the barrier attendant, who lives in Northam and was a casual volunteer, had been working trackside at around 4.30pm near the 500m mark when he was struck.
Race caller Darren McAullay told Radio 6PR's Oliver Peterson the crowd at Northam Races the storm had "come from nowhere".
"We all jumped due to the noise. It was just so loud. I was looking just around the 200 metre mark," he said.
"I looked up further beyond the track and there was people waving. I looked through the... binoculars and a man was laying on the track with a sand bucket tipped over.
"I immediately saw he was in a fair bit of trouble.
"Ambulance staff hightailed it up to where the man was working... the paramedics were on the scene in about 50 seconds.
"They applied CPR and they also gave him mouth-to-mouth before the ambulance put him onto the gurney.
"It was only a very small crowd... it's just ended on a tragic note.
"There is absolute pool of gloom over the place at the moment."
BOM duty forecaster Darryl Vink said there was no evidence of severe thunderstorm activity in Northam yesterday.
“It was nothing out of the ordinary,” he said.
“There was not a lot of rainfall around Northam yesterday.
“There was between 1mm and 15mm recorded, depending on where you were.”
He said York received 13mm and about 1.8mm was recorded at Toodyay.
The strongest wind gusts recorded in Northam were at 4.45pm on Thursday afternoon, travelling at 76km/h.
Mr Vink said thunderstorms were not uncommon this time of year.
“Spring is inherently an unstable time of year,” he said.
“We had not put a warning out in Northam yesterday because there was no evidence of severe thunderstorms.”
He said a thunderstorm would be classed as severe if it had elements of flash flooding, heavy rainfall, large hail or wind gusts of 90km/h or more.
Racing and Wagering Western Australia chief executive officer Richard Burt confirmed the Northam race track worker was taken to hospital.
"A Northam Race Club worker at today's Northam race meeting suffered a heart attack," he said.
"He has been taken by ambulance to hospital and is under medical care."
