Two men have died and several more have been injured in an explosion at the Morley Galleria shopping centre in Perth's north-east.

It is believed a power transformer exploded just after 9:30am on Tuesday.

A 30-year-old man died at the scene and three others with serious burns injuries were taken to Royal Perth Hospital.

One of those has since died.

Another person was taken to the Queen Elizabeth II Medical Centre due to smoke inhalation.

Six others were hurt but their injuries were not considered life-threatening and they were treated at the scene.

Harry Barugh said he was walking near the shopping centre when the incident happened.

"I thought a car had exploded, petrol ... but it was a lot worse than that, it was the worst sight I had seen in my entire life," he said.

"It was just 'whoosh' and then there were these guys just coming out and hitting the deck and then ripping their gear off."

Witness describes men on fire running from the building

Jonathon McDonagh was driving into the shopping centre car park when he saw the men on fire running from a doorway.

"It's not a nice thing to see, especially when you see people on fire," he said.

"I was just coming in the driveway... and they came running out, then everyone just started giving them a hand out and got them put out.

"I thought it was a joke to start out, but then I saw the doorway they came running from and I knew straight away - power station - something had to have happened.

"They were on fire, of course they were screaming."

Mr McDonagh said bystanders filled any containers they could find with water from a nearby fire hydrant to douse the men.

He emptied a bag from his utility and carried water in it, while others threw wet T-shirts over the men.

Sorry, this video has expired Witnesses describe shopping centre explosion

"Some other man, he emptied out his whole tool box and he used his tool box as a water supply to try to put them out, it was horrific," he said.

"By the time I had him out there was fire brigade, ambulance, there was other fellas on the ground, they were put out.

"I was holding the big bag trying to pour the water over him and he was crying on the ground with pain."

Mr Barugh described the response of those nearby as "fantastic".

"If there was anything good that came out of this morning, it was the commitment of Australian housewives with kids in pushers ... the working class of our country, and you should have seen, before the police boys and the ambulance boys, before anybody got here, their response, I'll never forget that, their response was fantastic."

Investigation into cause underway

Police Inspector Rob Harrison said the exact cause of the incident had not been established but the injured people had been working in an area near an electrical transformer.

"We believe that they possibly were workers who were working within that transformer area of the shopping centre," he said.

Inspector Harrison said police would be working with WorkSafe and EnergySafety to determine the cause and a report would be prepared for the coroner.

Emergency crews at the scene of an explosion at the Galleria shopping centre in Morley. ( ABC News: Emily Piesse )

Electrical company High Energy Service said some of its workers were on site completing maintenance work on Tuesday morning, but could not confirm if any had been injured in the incident.

Federation Centres, which operates the Galleria, described the incident as tragic.

General Manager Stephen Beer said part of the centre would remain closed while investigations were completed.

"We are focussed on doing all that we can to assist emergency services and as such we are unable at this stage to comment any further," he said.

"Our thoughts are very much with those involved and their families at this time."

He said regular maintenance work was being done at the time of the incident and it was not related to power outages caused by electrical storms across Perth on Monday.