How could surveillance balloon have travelled from China?
The Chinese authorities say a surveillance balloon sighted over sensitive US territory is one of theirs, but insist its purpose is for scientific research and that it has deviated off course.
We've looked at wind modelling data to see if its journey can be tracked.
Where has the balloon been seen?
US authorities say the balloon has been monitored travelling over Alaska's Aleutian Islands and across Canadian territory before appearing over the city of Billings in Montana on Wednesday, where it was spotted in the sky by city residents.