President Donald Trump warned Friday that a shutdown could last a "very long time" unless Democrats in the Senate join Republicans and approve funding for the border wall with Mexico.
Unless a last-minute deal is reached the government will shut down at midnight Washington time (1600 AEDT Saturday).
According to Democrats in the House and Senate, a shutdown would impact about 800,000 of the 2.1 million federal employees in the United States.
Some 380,000 federal workers would be furloughed -- put on unpaid leave -- including 52,000 employees of the Internal Revenue Service.
Some 80 percent of the employees of the National Park Service would also be sent home, along with 96 percent of NASA workers and 86 percent of the Commerce Department.
Another 420,000 workers considered essential personnel would work without pay including 41,000 federal law enforcement and correctional officers and others such as aviation and postal workers.
VP Mike Pence, right, walks with incoming White House Chief of Staff Mick Mulvaney and White House senior adviser Jared Kushner on talks to avert govt shutdown. Source: AAP
The departments impacted would include the homeland security, transport, commerce, state, agriculture, interior, treasury and housing and urban development.
Others such as the Defense Department, Department of Veterans Affairs and Department of Health and Human Services have already received funding and would be spared.
No visitor services would be provided at tourist attractions such as the nation's national parks, which are frequently visited over the Christmas holidays.
During the last shutdown, the Statue of Liberty was closed for two days before the state of New York decided to pony up the money necessary to keep it open.
The Smithsonian in Washington said that in the event of a shutdown, it had enough in reserve to keep its museums open through January 1.
There have been a number of government shutdowns in recent years including one which lasted three days under Trump in January.
An October 2013 shutdown lasted 16 days while one in 1995-96 lasted a record 21 days.
One person who would not be the victim of the shutdown is Special Counsel Robert Mueller, the target of Trump's frequent ire.
Mueller's team, which is investigating whether Trump's campaign colluded with Russia to get him elected, will continue working.
