US President Donald Trump has cancelled his delegation's trip to the World Economic Forum in Davos, Switzerland, next week due to the ongoing partial government shutdown.

Press Secretary Sarah Sanders said in a statement on Thursday that Trump made the move "out of consideration for the 800,000 great American workers not receiving pay and to ensure his team can assist as needed".

Trump, who attended last year's Davos event, had planned to go again this year, but pulled out last week as he grapples with Democrats in Congress over funding for a wall on the border with Mexico that has led to the shutdown.

Treasury Secretary Steven Mnuchin and Secretary of State Mike Pompeo were expected to lead the US delegation in Trump's place, two senior administration officials said this week.

Mnuchin and Pompeo had planned to speak jointly at the opening session of the forum on January 22.

They were also expected to jointly host a dinner of the Group of Seven foreign and finance ministers to discuss national security and economic issues.

Commerce Secretary Wilbur Ross and US Trade Representative Robert Lighthizer also planned to be part of the delegation.

Pelosi's 'excursion'

Earlier on Thursday, Trump also cancelled his Democratic opponent Nancy Pelosi's trips.

In a letter laced with sarcasm, Trump told House Speaker Pelosi: "I am sorry to inform you that your trip to Brussels, Egypt, and Afghanistan has been postponed. We will reschedule this seven-day excursion when the Shutdown is over."

"I am sure you would agree that postponing this public relations event is appropriate," he wrote.

Pelosi and her delegation had planned a non-publicised trip to Afghanistan - an active war zone - and were due to travel by a US Air Force plane. Her office said Egypt was not on the itinerary.

According to a congressional aide, several politicians were already loaded onto buses preparing to leave the US Capitol on Thursday when Trump pulled the plug.

Trump said that Pelosi could still book her own non-government flights.

"Obviously, if you would like to make your journey by flying commercial, that would certainly be your prerogative," he wrote.

The cancellation followed Pelosi's suggestion that Trump postpones his January 29 State of the Union address to Congress, or do it from the White House instead.