Washington DC - A federal judge on Thursday extended an order barring construction of President Donald Trump's White House ballroom but gave the green light for work to proceed on a proposed underground bunker.

District Judge Richard Leon ordered a halt last month to Trump's $400 million ballroom, ruling that congressional approval is needed for the project, which has already seen the historic East Wing torn down.

In an amended order on Thursday, Leon extended his ban on any above-ground construction of the proposed ballroom on the former site of the East Wing, which previously housed the offices of the First Lady.

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But he said building of a proposed underground national security facility can go ahead.

"Below-ground construction may proceed, including the construction of any 'top-secret excavations, bunkers, bomb shelters, protective partitioning, military installations, and hospital and medical facilities,'" the judge said.

Work can continue on the underground bunker provided it does "not lock in the above-ground size and scale of the ballroom," he said.

"National security is not a blank check to proceed with otherwise unlawful activity," he added.

The judge stayed his order for one week to allow the administration to appeal.

In his initial ruling halting the ballroom project, Leon said the president is a "steward" of the White House. "He is not, however, the owner!" he said.