[azurezyq]

Well, weather balloons don't have very sophisticated thousand-miles communication systems, nor China has the ability to deploy tracking stations in the US. I think China may know a balloon flew into Pacific and disappeared from the radar but appearing in the US may really be unexpected. Just like https://en.wikipedia.org/wiki/Fu-Go_balloon_bomb, you can have a balloon "travel" to the other side of the globe, but controlling or tracking it is another thing...

[signatoremo]

Shouldn’t they know when they lost it and alert other countries accordingly?

[azurezyq]

It's civilian and... I don't think there's a rule for that. Most balloons don't fly that far. For the WW2 Japanese case, which was designed for the purpose, only single digit percentage arrived in the other continent.

[signatoremo]

Well, that’s very doubtful. It’s a big and sophisticated balloon, and likely expensive, not an amateur one. Ww2 was 70 years ago, tracking has gone up by leaps and bounds since then.

But assuming for a second that they did lose it, the only responsible action would be to notify the authority, in China and other countries on its potential trajectory. Such a big object can be hazardous to air traffic if left untracked. It’s very hard to believe some innocent party just sent it up, lost it, didn’t tell anyone, not even its own country’s authority. Malicious intent is lot more plausible. Especially if the 2nd balloon over South America is confirmed.