Thousands of flights will be cancelled starting Friday in the United States due to the protracted budget impasse amid political confrontation between Republicans and Democrats.

The US government announced Wednesday that it would ask airlines to cancel flights starting Friday to "reduce pressure" on air traffic control, which is facing more absences due to the "shutdown".

"We will reduce flight capacity by 10% at 40 of the country's busiest airports," Transport Minister Sean Duffy told a press conference.

The official list of affected airports is due to be published later on Thursday, but according to US media the number of flights will be reduced at airports in Chicago, Dallas, Los Angeles, New York, Miami and Washington among others.

International flights are not affected by this measure, a source, speaking on condition of anonymity, told ABC News.

United Airlines issued a statement saying that long-haul international flights and those between connecting hubs would not be affected.

Flight reductions will start at 4% on Friday and gradually reach 10%, according to US media.

"We are short 2,000 air traffic controllers," the Transport Minister explained on Wednesday, adding that it was necessary to "reduce the pressure" by decreasing the number of flights to be supervised by the teams.

The United States entered its 36th day of budget impasse on Wednesday, breaking the record for the longest "shutdown" in the country's history.

Republicans and Democrats have been unable to agree on a new budget since October 1st.

As a result, hundreds of thousands of federal employees are furloughed while hundreds of thousands more are forced to continue working. They will not receive pay until the end of the crisis.

More than 60,000 air traffic controllers and transport security officers are in the second situation. And rather than work without pay for several weeks, some are not showing up for their posts.

- "Very unusual" -

The announcement by authorities of the cancellation of a significant number of flights comes ahead of a weekend conducive to air travel, with Tuesday, November 11 being a holiday in the United States.

It risks reinforcing the unpopularity of the "shutdown" in public opinion, in the wake of several key elections, where the Democratic opposition has scored large victories.

Minister Sean Duffy warned on Tuesday of the risks of "chaos": "You may see us close parts of the airspace, simply because we won't be able to manage it, due to a lack of air traffic controllers," he said, placing the blame on the Democrats.

"We will ask airlines to work with us to reduce their flight plans," said FAA chief Bryan Bedford on Wednesday.

"The aim is to prevent the situation from deteriorating," he added, standing next to the minister.

Airlines for America, a trade association representing many major U.S. airlines, said in a statement that it would seek to "mitigate the impacts for passengers".

Bryan Bedford said he did not recall such a reduction ever being decreed "during (his) 35-year career in the airline industry".

"This is a very unusual situation. Our controllers haven't been paid for a month. We're eager to be able to work normally again."

"The controllers who keep coming in are doing overtime, working more days (...) and we want to reduce this pressure (on them, editor's note) before it becomes a problem," Mr. Bedford continued.

On average, 44,000 flights are supervised by the FAA each day, according to its website.

More than 10,000 flights to and from the United States experienced delays last weekend, according to the FlightAware tracking service.

AFP