US President Donald Trump confirmed on Wednesday that the White House's iconic East Wing is being torn down in its entirety to make way for a huge US$300-million ballroom – a far more extensive demolition than previously announced.

Trump told reporters at an Oval Office event that he had decided after consulting architects that "really knocking it down" was preferable to a partial demolition.

The president was asked about the work at an event alongside Nato Secretary General Mark Rutte, after a mechanical excavator was photographed ripping through the East Wing's facade, leaving a tangle of broken masonry, rubble and steel wires.

The East Wing is where US first ladies have traditionally had their offices. The president works in the West Wing and the couple live in the Executive Mansion.

Trump says the new 90,000-square-foot ballroom with a capacity of 1,000 people is needed to host large state dinners and other events that currently have to be held in a tent.

Trump's comments on Wednesday put the cost of the demolition at US$300 million, raising the cost from the US$250 million quoted by the White House days ago.

While the US president said that the East Wing is "completely separate from the White House itself," it is in fact physically joined to the main mansion by a covered colonnade.

The facelift has raised questions about what critics have decried as a lack of transparency, and has led to complaints that there was no advance notice or consultation.

"We are deeply concerned that the massing and height of the proposed new construction will overwhelm the White House itself – (which) is 55,000 square feet – and may also permanently disrupt the carefully balanced classical design of the White House with its two smaller, and lower, East and West Wings," the National Trust for Historic Preservation said in a letter to the Trump administration on Tuesday. (AFP)