A US military fighter jet shot down a suspected Chinese spy balloon off the coast of South Carolina on Saturday, a week after it entered US airspace and triggered a dramatic - and public - spying saga that worsened Sino-US relations.

President Joe Biden said he had issued an order on Wednesday to take down the balloon, but the Pentagon had recommended waiting until it could be done over open water to safeguard civilians from debris crashing to Earth.

"They successfully took it down, and I want to compliment our aviators who did it," Biden said.

Multiple fighter and refuelling aircraft were involved in the mission, but only one - an F-22 fighter jet from Langley Air Force Base in Virginia - took the shot at 2.39pm (1939 GMT), using a single AIM-9X supersonic, heat-seeking, air-to-air missile, a senior US military official said.

The balloon was shot down about six nautical miles off the US coast, over relatively shallow water, potentially aiding efforts to recover elements of the Chinese surveillance equipment in the coming days, officials said.

The shootdown came shortly after the US government ordered a halt to flights in and out of three regional airports - Wilmington, Myrtle Beach and Charleston - due to what it said at the time was an undisclosed "national security effort." The flights resumed on Saturday afternoon.

While Saturday's shootdown concludes the military dimension to the spying saga, Biden is likely to continue to face intense political scrutiny from Republican opponents in Congress who argue he failed to act quickly enough.

Questions also remain about how much information China may have gathered during the balloon's trek across the United States.

The balloon first entered US airspace in Alaska on Jan 28 before moving into Canadian airspace on Monday, Jan 30. It then re-entered US airspace over northern Idaho on Jan 31, a US defence official said. Once it crossed over US land, it did not return to the open waters, making a shootdown difficult.

US officials did not publicly disclose the balloon's presence over the United States until Thursday.

"It's clear the Biden administration had hoped to hide this national security failure from Congress and the American people," said US representative Mike Rogers, a Republican who leads the House Armed Services Committee.

‘Clear violation’

Biden's emphasis on Saturday that - days ago - he ordered the balloon shot down as soon as possible could be an effort to respond to such critics.

Former president Donald Trump, Biden's potential rival in the 2024 election, called earlier this week for the balloon to be shot down, and has sought to portray himself as stronger than Biden on China. The US relationship with China is likely to be a major theme of the 2024 presidential race.

Washington had called the balloon's appearance a "clear violation" of US sovereignty and notified Beijing about the shootdown on Saturday, a US official said.

Still, officials on Saturday appeared to play down the balloon's impact on US national security.

"Our assessment - and we're going to learn more as we pick up the debris - was that it was not likely to provide significant additive value over and above other (Chinese) intel capability, such as satellites in low-Earth orbit," the senior US defence official said.

A Reuters photographer who witnessed the shootdown said a stream came from a jet and hit the balloon, but there was no explosion. It then began to fall.

China expressed regret that an "airship" used for civilian meteorological and other scientific purposes had strayed into US airspace.

China's foreign ministry said on Saturday that the flight of the airship over the United States was a force majeure accident, and accused US politicians and media of taking advantage of the situation to discredit Beijing.

The Pentagon assesses that this balloon was part of a fleet of Chinese spy balloons. On Friday, it said another Chinese balloon was flying over Latin America.

"Over the past several years, Chinese balloons have previously been spotted over countries across five continents, including in East Asia, South Asia and Europe," the US official said. The suspected spy balloon prompted US Secretary of State Antony Blinken to postpone a visit to China this week that had been expected to start on Friday.

The postponement of Blinken's trip, which had been agreed to in November by Biden and Chinese President Xi Jinping, was a blow to those who saw it as an overdue opportunity to stabilise an increasingly fractious relationship between the two countries.

China is keen for a stable US relationship so it can focus on its economy, battered by the now-abandoned zero-Covid policy and neglected by foreign investors alarmed by what they see as a return of state intervention in the market.

- Reuters