President Joe Biden on Monday defended the decision to wait until a Chinese balloon crossed the United States before shooting it down, and the White House said valuable intelligence was being culled from the device.

China says the balloon was an errant weather observation aircraft with no military purpose, but Washington has described it as a sophisticated high-altitude spying vehicle.

A US fighter plane shot down the balloon Saturday just off the east coast in the Atlantic and naval and coast guard forces are currently recovering the debris for intelligence analysis.

"Once it came over the United States from Canada, I told the Defense Department I wanted to shoot it down as soon as it was appropriate," Biden told reporters.

"They concluded we should not shoot it down over land. It was not a serious threat and we should wait till it got (over) the water."

National Security Council spokesman John Kirby said US personnel "have recovered some remnants off the surface of the sea," although weather conditions have not permitted much undersea surveillance of the debris field.

They will "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," Kirby said.

Measures were taken to ensure the balloon's instruments were "mitigated" in their ability to spy during the flyover, while "at the same time increasing and improving our ability to collect intelligence and information from it," Kirby added.

"We're still analyzing the information that we were able to collect off of the balloon before we shot it out of the sky and now we're going to recover it and I suspect we may learn even more."

Biden, who has tried to establish more stability in the relationship with China, said he was not surprised by the balloon incident.

"The question of the balloon and attempting to spy on the United States is something that is anticipated from China," he said.

"It's not a question of trusting China, it's a question of deciding where we can work together and where we have opposition."

- Huge balloon and payload -
After slowly traversing the middle of the United States, reportedly over several top secret military sites, the balloon headed out over the east coast, where it was downed.

General Glen VanHerck, head of the US Northern Command, told reporters that a naval ship is in the process of mapping the debris field, which is expected to measure about 1,500 by 1,500 meters (yards) in the Atlantic.

The balloon itself was up to 200 feet (60 meters) tall and carried a payload weighing several thousand pounds that was roughly the size of a regional jet aircraft, he said.

According to Kirby, there was no intention to send the pieces back to China. "I know of no such intention or plans to return it," he said.

And VanHerck said the balloon debris would be carefully studied.

"I don't know where the debris is going to go for a final analysis, but I will tell you that certainly the intel community along with the law enforcement community that works this under counterintelligence will take a good look at it," he said.

One detail already known, Kirby said, is that the balloon was not merely drifting but had propellers and steering to give a measure of control, even as it was swept along in high altitude jet stream winds.

"It is true that this balloon had the ability to maneuver itself -- to speed up, to slow down and to turn. So it had propellers, it had a rudder, if you will, to allow it to change direction," he said.