There are reports of widespread delays at US airports due to shortages of air traffic control staff linked to the US government shutdown.
A federal closure, the longest in history, has meant that controllers are currently working without pay.
Nancy Pelosi, the leader of the House of Representatives, has blamed President Trump for the disruption.
The delays come one day after a stark warning was issued by air industry unions about the risk to public safety.
“In our risk averse industry, we cannot even calculate the level of risk currently at play, nor predict the point at which the entire system will break,” air traffic, pilot and flight attendant union leaders said in a joint statement.
In total about 800,000 employees have been working without pay, or have been temporarily laid off, since areas of the federal government shut down due to lack of funding 35 days ago.
Mr Trump has refused to approve any new funding agreement that does not include $5.7bn (£4.4bn) for his southern border wall.
Democrats in Congress refuse to approve wall funding, so the two sides are stuck at an impasse.
In a tweet on Friday, Mrs Pelosi appealed to the president to “stop endangering the safety, security and well-being of our nation” and reopen the government.
How bad is the flight disruption?
Flights were halted at New York’s LaGuardia airport – the 20th busiest in the country – shortly before 10:00 local time (15:00 GMT).
The US Federal Aviation Administration (FAA) has now confirmed the temporary ground stop has been lifted.
In a statement, the FAA said a “slight increase” in sick leave absences at two air traffic control facilities had led to the schedule changes – which it said was to ensure safety levels were maintained.
It said departure delays at Philadelphia, Newark and LaGuardia were linked to the shortages.
The FAA has advised the public to check with individual airlines for more information.
LaGuardia, situated in the New York city borough of Queens, is used by about 30 million passengers every year.
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