The US Secret Service allegedly had to destroy an entire top-secret command centre after Donald Trump invited Malcolm Turnbull into a room reserved only for the most trusted agents.

The shocking claims have been revealed in Fear: Trump in the White House, legendary journalist Bob Woodward's scathing best-selling book that exposes life inside the Trump administration.

The botched meeting is said to have taken place at the G20 summit in Hamburg in July 2017 when Trump arranged talks with Turnbull.

In violation of security rules, the US President invited the former PM into his Sensitive Compartmented Information Facility.

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A Sensitive Compartmented Information Facility (SCIF) is an enclosed space specifically intended for use with national security and defence purposes.

Similar to a vault, it contains hardened computers and communication equipment that processes and decodes classified information.

The facility in Hamburg was a large steel room and only those with the highest US security clearances were able to enter to prevent someone planting listening devices.

As Turnbull did not have security clearance, Woodward alleges, the steel room had to be torn down.

Trump allegedly later joked with Turnbull that his security guys "were so pissed" about his blunder. "They couldn't believe I did it," Woodward alleges Trump told the former PM.

During the Hamburg meeting, Turnbull allegedly urged the US President to exempt Australian steel from tariffs, saying Australia "was in every battle with you".

"We do this steel that's specialty steel," the book claims Turnbull said.

"We're the only one that produces it in the world. You've got to let us out. You've got a $40 billion trade surplus with us. We're military allies with you. We're in every battle with you."

Trump reportedly replied: "Of course, we'll let you out. That makes total sense. You guys are great. We've got a big surplus with you guys."

However, he denied the conversation had occurred when White House staffers brought it up during Turnbull's Washington visit eight months later.

The US President then reportedly backtracked and admitted he had actually vowed to make Australia exempt when Turnbull reminded him of their meeting inside the secure facility.