Government officials have been monitoring what is believed to be a Chinese spy balloon. It's been floating over the northern United States for a few days, according to a news report Thursday.

Pentagon officials debated shooting the balloon down after the balloon was spotted over Billings, Montana, on Wednesday. An unnamed senior defense official told NBC News that the balloon is still over the U.S. but declined to say where it is now.

“The United States government has detected and is tracking a high-altitude surveillance balloon that is over the continental United States right now,” Pentagon Spokesperson Brig. Gen. Pat Ryder told the outlet. “We continue to track and monitor it closely. Once the balloon was detected, the U.S. government acted immediately to protect against the collection of sensitive information."

The official said the balloon does not pose a threat to civil aviation because of its altitude, and the decision to not shoot the balloon down was because of a safety risk. China has not said whether the balloon belonged to them.

This story is developing — check back for updates.