The UK has Typhoon fighter jets on call 24/7 to tackle the threat of spy balloons, Rishi Sunak has said.
But the Prime Minister declined to say if any such devices had been detected in UK airspace after Transport Minister Richard Holden said it was "possible".
It follows four concerned instances in North America amid fears of spying by the Chinese government.
No 10 said the UK is "well prepared" to deal with threats, after Defence Secretary Ben Wallace announced plans to assess the dangers posed by the balloons.
Mr Sunak said: "I want people to know that we will do whatever it takes to keep the country safe.
"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 and, as I said, we will do whatever it takes to keep the country safe."
When pressed about whether there had been any incidents in UK airspace, the Prime Minister added: "As I said, I wouldn't comment in detail on security matters but people should be reassured that we have all the capabilities in place to keep the country safe."
This morning Mr Holden admitted the UK is "concerned about what's going on" in the US.
He added: "China is a hostile state and we need to be aware of that and the way it acts and behaves.
"I think there was an era when China could have gone a different way and perhaps opened up. But it is quite clear at the moment that it is not going in that direction and we have got to be really robust in our dealings with China."
It comes after Mr Wallace said: "The UK and her allies will review what these airspace intrusions mean for our security."
US fighter jets shot down an "unidentified object" over Lake Huron on Sunday - the fourth object to enter US or Canadian airspace in just over a week.
On February 4, the US military downed a suspected Chinese spy balloon off the Carolina coast after it traversed sensitive military sites across North America.
Almost a week later on Friday, they shot down an unknown "car-sized" object flying in US airspace off the coast of Alaska.
Canadian Prime Minister Justin Trudeau said on Saturday that he ordered a US warplane to shoot down an unidentified object that was flying high over northern Canada.
Yesterday a further unidentified object was shot down with a missile by US fighter jets over Lake Huron.
Tobias Ellwood, the Conservative chairman of the Commons Defence Select Committee, said China was "exploiting the West's weakness" with the potential spy balloons.
The former defence minister told Times Radio: "I think this is a testament as to where China is going.
"It is interpreting our wobbly international rules-based order to its own benefit.
"It is exploiting the West's weakness, it is joining together with Russia, quietly, to try and weaken the West, to weaken the United States in particular so it can thrive itself.
"That is the new economic battlefield that we now see."
