A suspected Chinese surveillance balloon shot down off the US coast was about 200 ft (60m) tall and carrying an airliner-sized load, officials say.
At a briefing on Monday, a US defence official said the size and make-up of the object informed the decision not to shoot it down while it was over land.
"Picture large debris weighing hundreds if not thousands of pounds falling out of the sky," Gen Glen VanHerck said.
The US is still working to recover debris off the coast of South Carolina.
Remnants of the object - which the US believes is a spy balloon but China says is a weather monitoring device blown astray - have been collected from a roughly 1,500m (4,920 ft) by 1,500m sized area, but it is thought debris is spread over a far larger site.
Multiple fighter jets were involved in the operation to shoot it down, but only one US Air Force F-22 took the shot at 14:39 local time (19:39 GMT) on Saturday days after it first appeared over US territory. It sent debris hurtling down about six nautical miles off the US coast.
"They have recovered some remnants off the surface of the sea and weather conditions did not permit much undersea surveillance of the debris field," National Security Council spokesman John Kirby said on Monday.
He said US personnel would "in the coming days be able to get down there and take a better look at what's on the bottom of the ocean, but it's just started".
There is no plan to give the remnants back to China, officials said, adding that the retrieved debris would be analysed by intelligence experts.
A number of specialist ships have been deployed to the area, including an oceanographic survey ship that uses sonar and other means to map out a debris field, Gen VanHerck, who commands both the US military's Northern Command and joint US-Canadian North American Aerospace Command, or Norad, said.
He added that while the balloon was several hundred feet tall, the payload - the portion which would have carried equipment - was about the same size as a regional airliner.
Gen VanHerck said the US was still working to determine whether the debris includes potentially dangerous materials, such as explosives or battery components.
Republican politicians have accused US President Joe Biden of a dereliction of duty for allowing the balloon to traverse the country unhindered.
The decision to shoot it down also triggered a diplomatic spat between the US and China, and prompted Secretary of State Antony Blinken to cancel a scheduled trip to Beijing that had been aimed at easing tensions.
On Monday, China accused the US of using "indiscriminate force" when it downed the balloon. It said it "obviously overreacted and seriously violated the spirit of international law".
The US believes the balloon was being used to monitor sensitive military sites.
Adm Mike Mullen, former chair of the US Joint Chiefs of Staff, rejected China's suggestion it might have blown off course, saying it was manoeuvrable because "it has propellers on it".
"This was not an accident. This was deliberate. It was intelligence," he added.
A Chinese foreign ministry spokesperson has confirmed that a second balloon - currently floating over Latin America - is also Chinese.