The bomb squad has destroyed a suspicious package at historic Fremantle Prison after a former prisoner contacted authorities claiming explosives were hidden beneath a wooden floor.

Western Australian police said the bomb squad was called to the former prison on Tuesday and discovered the package, believed to be at least 25 years old.

The ABC understands a former prisoner contacted Fremantle Prison staff and informed them that explosives were hidden beneath a cell in the former solitary confinement unit.

Staff have told the ABC the area was evacuated on Tuesday while the bomb squad inspected the cell.

The package was destroyed on site but police are yet to confirm whether or not it contained explosives.

The prison has hosted more than three million visitors since opening as a tourist attraction to the public in 1992.

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The former Fremantle prisoner, who is believed to still be incarcerated in another prison, claimed that while an inmate in the 1980s, he knew someone had hidden explosives under floorboards of a cell.

The prison's executive manager Bevan Beaver said the bomb squad was then called in.

"They came down, investigated, found a substance, they buried it, and exploded it," he said.

"They didn't want to take it away on precaution; they didn't know what it was so they just buried it. It was in a bag, they didn't uncover the bag, they just took [it] as it was, and buried it.

"We don't know what it was at this stage."

Mr Beaver said there was no danger to anyone, although tourists are taken past the cells where the package was found.

"The bomb squad came in and did their job very professionally," he said.

"There was no danger to any public or staff member.

"It is part of our tourist route but they don't go into those cells so they would have walked past it but not over it."

The cell in question had been used as a solitary confinement unit, but was later used for art therapy and art supply storage.

Riots, executions and tours

The Fremantle Prison was decommissioned as a maximum security jail in 1991, after being in use for almost 140 years.

More than 40 prisoners were executed at Fremantle Prison between 1889 and 1964.

In 1988, prisoners rioted, setting fire to parts of the prison, taking some prison officers hostage and making demands about conditions.

In 1991, inmates and staff were transferred to a new maximum security prison at Casuarina, south of Perth.

Since 1992, tours have operated out of the prison and it has become one of the state's most popular tourist attractions.