The US government has partially shut down for the first time in 17 years, after Congress failed to agree measures to continue funding basic services.
Federal agencies ordered the closure to begin at midnight on Tuesday (04:00 GMT), meaning 800,000 "non-essential" workers have been forced to stay at home.
The shutdown began after the law to fund government ran out, as the Republican-led House of Representatives attempted to draw up a replacement that blocks parts of President Barack Obama's signature healthcare law.
The House has passed two spending bills in recent days, both of which have been rejected by the Democrat-led Senate.
The House asked for a conference on the budget with the Senate, but the upper house of Congress killed that proposal when it met on Tuesday morning.
Senate majority leader Harry Reid, a Democrat, said that he would not negotiate as long as the House linked the budget law to the healthcare law.
Tuesday's Senate vote was the fourth time since this political battle began that the body had rejected a House Republican bill or proposal.
Some critical parts of the government, including the military and air traffic control, will remain open. The shutdown will, however, keep hundreds of thousands of federal workers at home and unpaid.
It could affect government services including park management, food assistance for children and pregnant women and federal home loan programmes. Federal agencies, such as NASA, the Environmental Protection Agency (EPA) and others, were also affected.
Obama spoke bluntly about House Republicans: "You don't get to extract a ransom for doing your job, for doing what you're supposed to be doing anyway, or just because there's a law there that you don't like."
Speaking of the health care law that undergoes a major expansion on Tuesday, he said: "That funding is already in place. You can't shut it down."
Signs of dissent
The Republican speaker of the House, John Boehner, responded a few hours later on the House floor. "The American people don't want a shutdown and neither do I," he said. However, he added, the new health care law was having "a devastating impact ... something has to be done".
House Republicans have sought a year's delay in a requirement in the health care law for individuals to buy coverage.
However, in recent days several Republican senators and House members have said they would be willing to vote for straightforward legislation with no healthcare-related provisions.
The last shutdown, in the winter of 1995-96, severely damaged Republican election prospects.
Stock markets around the world reacted resiliently to the shutdown on Tuesday morning, with analysts saying significant damage to the US economy was unlikely unless the shutdown lasted more than a few days. After falling the day before the US shutdown deadline, European stocks mostly recovered. In Asia, stocks were mixed, while Wall Street was expected to open slightly higher.