US President Donald Trump on Monday confirmed that work was underway to build a "beautiful" new helipad at the White House, in his latest personally directed redesign to the iconic building.

The helipad is situated on the South Lawn, where presidents and their family for decades have been photographed strolling across the grass to board or exit awaiting "Marine One" helicopters.

The contractor has been asked to speed up work to be finished ahead of an upcoming state visit, apparently that of Chinese President Xi Jinping in September, the Washington Post reported.

"So now we're building a helipad, beautiful helipad, and it's got the seal of the White House on it -- in granite, carved granite, it's... really a beautiful thing," Trump told reporters.

The landing site aims to solve problems associated with the new fleet of presidential helicopters built by Sikorsky, Trump said.

While it has been widely reported that the helicopters' exhaust scorches grass, Trump added Monday that the airflow is so powerful, the lawn actually "gets ripped out."

"So they landed the helicopter, and half of the grass was sitting in front of the Oval Office front door. The rest of it was scattered all over," he said.

Sikorsky has agreed to pay for the project, Trump said, because the company felt "a little guilty" about the lawn issue.

"It's about $5 or $6 million -- they're paying the full cost, and when I heard they were paying the cost, I went out and said, 'let's do a beauty, let's not just do a piece of concrete and paint it white,'" he said.

The Post however reported a project cost of at least double -- $13 million -- which also includes renovations of the South Portico and adjacent driveway.

- Corinthian columns -

Simultaneously, work is continuing on a much larger White House project -- Trump's addition of a massive ballroom.

The project has seen Trump tear down the historic East Wing, and has prompted a legal dispute over major alterations going ahead without congressional approval.

Speaking later to a group in the historic White House Rose Garden -- which Trump has remade into a patio similar to his Mar-a-Lago estate in Florida -- he lamented the lawsuits.

"In this world we're living, especially if your name is Trump, you get sued," he said.

He claimed that the legal suit had led to a top secret "tremendous military center" being built under the ballroom to be revealed.

He has also hinted at changes to the North Portico's 200-year-old columns -- which are in the Ionic style and not his preferred, more ornate Corinthian style -- and have recently been covered by scaffolding.

Over the weekend he posted apparent architectural mock-ups of Corinthian columns replete with lions' heads, on the White House.