WASHINGTON:  Twenty-four hours before he takes the oath of office as the 45th US president, Donald Trump arrived in Washington on Thursday, determined to transform American politics over the next four years.

The Republican billionaire's arrival caps an extraordinary and improbable run for the White House that, once he takes the reins from President Barack Obama, will launch the United States into a new era.

"The journey begins and I will be working and fighting very hard to make it a great journey for the American people," Trump tweeted before leaving Trump Tower, his Manhattan home.

The 70-year-old president-elect traveled aboard an official government jet to a military base near Washington with his wife Melania. The pair exited the plane and headed into the nation's capital for a day of pre-inaugural festivities.

"It is a momentous day before a historic day," said Vice President-elect Mike Pence, as Washington put its finishing touches on the downtown area where hundreds of thousands of Americans will congregate for Trump's inauguration.