The US did not detect previous high-altitude Chinese alleged 'spy' balloons until they left US airspace, according to The Wall Street Journal, citing White House officials.

Chinese officials stated repeatedly over the past week that the balloon was of a civilian nature, and that the reports regarding its nature were greatly inflated by the US.
 
Reports cited defense officials saying that at least three suspected Chinese balloons flew over the continental United States during the Trump administration and at least one previously during the Biden administration, raising questions about how they were handled and why the latest incident was not avoided.
 
Senior administration officials stated that the flights were much shorter, reducing the window for detection, and much of the intelligence was discovered after the fact. They refused to go into detail about how the balloons were detected in the previous four instances.
 
They went on to say that intelligence agencies are preparing to brief key members of the previous Trump administration. Trump's national security advisors, John Bolton, H.R. McMaster, and Robert O'Brien, have stated that they were unaware of any security breaches caused by Chinese balloons.
 
The Chinese balloon entered US airspace on January 28 for the first time. It was spotted last Wednesday by civilians hovering over Montana, which is home to several nuclear missile sites, prompting the White House to publicly acknowledge the breach.

The Financial Times reported that Blinken canceled his trip to Beijing over the incident, hours before he was supposed to depart for China. Several US politicians and commentators have called for canceling the meeting over the accidental breach, including Nikki Hailey and Donald Trump.

A US fighter jet successfully brought down the alleged Chinese surveillance balloon in US territorial waters off the coast of South Carolina, US Defense Secretary Lloyd Austin announced on February 4th.

"This afternoon, at the direction of President Biden, US fighter aircraft assigned to US Northern Command successfully brought down the high altitude surveillance balloon launched by and belonging to the People’s Republic of China (PRC) over the water off the coast of South Carolina in US airspace," Austin said in a statement.

US President Joe Biden on Wednesday gave his authorization to neutralize the balloon as soon as the operation could be carried out "without undue risk to American lives under the balloon’s path," according to the statement.