Security concerns have been raised after a suspected Chinese spy balloon and three other unidentified objects were shot down over North America.

The incidents have seen simmering tensions between the United States and China burst into public view, and raised questions about the possibility of surveillance technologies or other objects flying in UK airspace.

China has denied the balloon was used for spying, but the incident will only inflate tensions between the Chinese Communist Party’s administration and the west.

When and where did it start?

US defence and military officials said a flying object – the suspected Chinese surveillance balloon – entered their country’s air defence zone on January 28 and moved largely over land across Alaska and then into Canadian airspace in the Northwest Territories, before crossing back into US territory.

The balloon reportedly flew over a number of sensitive military sites as it moved across North America, before it was shot down on February 4 off the east coast, six nautical miles off the South Carolina shore, on the orders of US President Joe Biden.

Since then, three other objects have been downed by the US: one off the coast of Alaska, one over Canada, and one over Lake Huron, one of the great lakes that divides the north-east of the US from Canada.

What do we know about the objects?

The first object, the suspected Chinese spy balloon, was a large white orb, estimated at 60 metres in height – which is roughly the width of a football pitch – and carried a long sensor package underneath about the size of a small jet, according to the head of North American Aerospace Defence Command and the US Northern Command, General Glen VanHerck. It was flying at about 60,000 feet.

Little is known about the other three unidentified objects, which are still being recovered, but they are reportedly smaller, one being described as car-sized.

General VanHerck said part of the reason for shooting the three down was a “heightened alert” following the initial balloon incident.

White House National Security Council spokesman John Kirby said the US did not yet have evidence that the three unidentified objects were equipped for spying purposes — or even belonged to China — but added officials have not ruled that out.

He said: “Because we have not been able to definitively assess what these most recent objects are, we acted out of an abundance of caution.”

The three unidentified objects were flying lower than the balloon, and Mr Kirby said they posed a risk to civilian aviation.

Was it aliens?

General VanHerck, when asked whether he had ruled out the possibility the three unidentified objects were extraterrestrials, said: “I haven’t ruled out anything at this point.”

But White House press secretary Karine Jean-Pierre sought to deflate such speculation, saying: “I know there’s been questions and concerns about this, but there is no, again, no, indication of aliens or extraterrestrial activity.”

Are there any spy balloons over the UK?

Transport minister Richard Holden has suggested that it is “possible” that Chinese spy balloons might already have been used over the UK.

But Prime Minister Rishi Sunak declined to be drawn on the possibility of similar incidents in UK airspace in an interview with broadcasters on February 13.

Defence Secretary Ben Wallace has announced Britain will conduct a security review into the issue.

Pilots reported at least seven near misses with objects which may have been balloons in UK airspace last year, but there is no suggestion such incidents related to technologies used by other states for spying.

But balloons are deliberately launched over the UK and elsewhere on a regular basis for scientific purposes. In October 2017, the Met Office said it “launches over 4,300 balloons every year from six locations across the UK” and is “involved in launching thousands more around the globe”.

Could the UK follow the lead of the US and shoot any objects down?

Mr Sunak said the Government would “do whatever it takes to keep the country safe”.

He said: “We have something called the quick reaction alert force which involves Typhoon planes, which are kept on 24/7 readiness to police our airspace, which is incredibly important.

“I can’t obviously comment in detail on national security matters, but we are in constant touch with our allies.”

How concerning are the objects?

The US has alleged that China’s People’s Liberation Army operates a fleet of balloons across the globe used specifically for spying. The US administration said balloons similar to the one shot down off its east coast have sailed over five continents.

But the US also insists the three unidentified objects did not pose a threat to US security and that even the large balloon provided “limited additive capabilities” to China’s other surveillance programmes.

Canadian Prime Minister Justin Trudeau said “there is some sort of pattern” to the balloon and three other objects, though the US has not echoed that claim.

China denies the balloon shot down by the US was used for surveillance, saying that it was an unmanned airship made for meteorological research that had been blown off course.

China also alleged that more than 10 US high-altitude balloons have flown in its airspace during the past year without its permission, but the US said it is not flying surveillance balloons over China.

Nato defence ministers, including Mr Wallace, are meeting in Brussels this week to discuss a range of issues, and spy balloons are said to now be on the agenda.

Announcing a security review following the US balloon incident, Mr Wallace said: “The UK and her allies will review what these airspace intrusions mean for our security. This development is another sign of how the global threat picture is changing for the worse.”

So everything is under control?

Former British ambassador to the US and national security adviser Lord Kim Darroch, when asked on Times Radio about the UK’s ability to intercept such objects, said: “We will have some capability; whether we have a watertight capability as the Prime Minister says, I’m not so sure.

“But we have enough capability, I think, that people can certainly sleep easy in their beds.”

He said people should “sleep easy” despite the threat of Chinese spy balloons because “an awful lot of that goes on everywhere”.

Asked about how concerning the balloon incident is, former chief of air staff Air Chief Marshal Sir Michael Graydon told LBC: “Until we know what’s actually in them they’re an irritation, certainly, and it’s highly likely it’s got some spy equipment on it but it would be very useful, wouldn’t it, to find out what’s in it before we get our knickers too much in the twist on that.”

Asked why China would bother with surveillance balloons when it already has satellites, he said: “It’s a very good question. That’s been sort of exercising my mind, what they are getting from a balloon that they can’t get from other sources is not clear to me at all, and probably we have enough information available from satellites which they are able to get on to, and frankly using Google and all the rest of it, would give them an awful lot of information.

“I think possibly there’s opportunity to listen in to certain things that they might not be able to do so easily.”