President Barack Obama has said a government shutdown that idles hundreds of thousands of workers and closes museums and parks nationwide was "completely preventable".
The US leader said he would try to get Congress to restart operations as soon as possible.
America woke up to the shutdown after a deeply polarised Congress failed to agree a new budget in a dispute over Mr Obama's signature health care law.
Mr Obama blames the shutdown on the Republicans"This shutdown was completely preventable. It should not have happened," Mr Obama said in a letter to government employees.
As the shutdown entered into force, "closed" signs and barricades sprang up at the Lincoln Memorial, museums and federal workplaces across the country.
The White House was operating with minimum staff, including household workers taking care of the first family's residence and presidential aides working in the West Wing.
The shutdown means non-essential services are closing.
That includes some of America's most famous tourist attractions, such as the Statue of Liberty and Ellis Island in New York, and Alcatraz Island near San Francisco.
Almost all of NASA shut down, except for Mission Control in Houston, and national parks closed along with the Smithsonian museums and the National Zoo. Even the zoo's popular panda cam went dark, shut off for the first time since a cub was born there in late August.
The shutdown affects national parks such as YellowstoneWorkers classified as essential government employees, such as air traffic controllers or Border Patrol agents, continue to work. Members of parliament are deemed essential and will also continue to work.
Up to 800,000 government employees are furloughed. More than a million others could be asked to work without pay.
It is the first US shutdown in 17 years, with analysts concerned about its potential impact on Wall Street and global markets.
A lot will depend on how long it takes politicians to bridge their differences – and there was no immediate sign of compromise on Capitol Hill.
The last shutdown, under the Clinton Administration, lasted 21 days between December 1995 and January 1996.
For now, Democrats and Republicans keep blaming each other.
The Republicans had insisted on delaying the healthcare reform – known as Obamacare - as a condition for passing a bill.
But this approach was rejected by allies of the president, in a series of back-and-forth moves between the Republican-controlled House and the Democrat-dominated Senate.
House Speaker John Boehner said Mr Obama refused to negotiateIn the last of such moves, the Senate reconvened in the morning and quickly rejected the House's call to form a negotiating committee to consider delaying the healthcare law in exchange for restarting the government.
Mr Obama's communications director, Jennifer Palmieri, said the White House was open to changes in the healthcare law in future negotiations, but not as part of passing a budget bill.
"What we're not going to do is entertain those kinds of solutions when there is a gun pointed to your head," Ms Palmieri told MSNBC.
The Republicans insisted the fault rested with Democrats who they said were unwilling to make any changes to Obamacare.
House Speaker John Boehner said he did not want a government shutdown, but added the health care law "is having a devastating impact. ... Something has to be done."
The Democrats accused the Republicans of succumbing to the Tea Party hard-line conservatives and seeking to gain political advantage at the expense of citizens.
Senate Majority Leader Harry Reid said: "The government is closed because of the irrationality of what's going on on the other side of the Capitol."
Meanwhile, Obamacare itself was unaffected and enrolment opened for millions of people shopping for medical insurance.
The president was to meet with citizens signing up for his healthcare programme and then make a lunch-hour speech in the Rose Garden.
The House of Liberty can be seen only from a distanceThe shutdown is likely to further alienate citizens already largely disillusioned by their ruling class and for the most part disappointed with the president's performance, according to the latest polls.
Marc Cevasco, who works in the Department of Veterans Affairs, said the uncertainty of how long the shutdown would last made his uneasy.
"Even if it's just shut down for a week that's a quarter of your pay this month. That means a lot to a lot of people," he said.
The political dysfunction at the Capitol also raised fresh concerns about whether Congress can meet a crucial mid-October deadline to raise the government's $16.7trn debt ceiling.
This would force the country to default on its obligations, dealing a potentially painful blow to the economy and sending shockwaves around global markets.