The US aviation regulator has stressed that air travel remains safe in the face of concerns voiced by unions over the country’s government shutdown.

Unions representing air traffic controllers, airline pilots and flight attendants warned of “serious safety concerns” in the air travel industry if the shutdown continues.

The shutdown has forced air traffic controllers, air marshals, transportation security administration officers, FBI agents, and other safety staff to work without pay, according to the unions.

“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. It is unprecedented,” according to the statement issued by presidents of the US National Air Traffic Controllers Association, Air Line Pilots Association and the Association of Flight Attendants.

The longest government shutdown in US government history has left a reported 800,000 federal staff without pay since December 22.

The Federal Aviation Administration responded to the unions’ concerns in a statement to USA Today.

The regulator said: “The FAA continually reviews and analyses the performance of the national airspace system to assess its safety and efficiency.

“We have not observed any appreciable difference in performance over the last several weeks compared to the same periods during the previous two years.

“We remain grateful to the air traffic controllers for their professional and dedication to their safety mission.”

The FAA added that it has seen no operational disruption and “no unusual increased absenteeism”.

Congress and the White House are locked in an impasse that has led to the longest government shutdown on record over president Donald Trump’s demands for $5.7 billion to build a wall along the US-Mexico border.