Speaking with reporters Thursday, Secretary of Defense Lloyd Austin said the United States had no plans to try to shoot down the rocket.
The roughly 100-foot-long remnant, a section that launched the main module of China's first space station, would be among the biggest space debris to fall to Earth.
Another organisation tracking the rocket pieces said it could touch down in the Tasman Sea, between New Zealand and Australia; Re-entry and debris experts at Aerospace Corporation, a U.S. government funded research and development centre predicted the re-entry for 3.26pm (NZ time) on Sunday.
Space-Track, using U.S. military data, tweeted that the window for re-entry is now predicted to be 0104-0304 GMT Sunday, but cautioned that the uncertainty about the timing made the location hard to pinpoint.
US Space Command released information online giving the projected time of reentry, but also says there is a window of plus or minus 60 minutes.
A Chinese foreign ministry spokesperson said on Friday that the probability of any harm is extremely low, as most of the rocket components will likely to burn up upon reentry.
"This is hard to predict and not an exact measurement", Space-Track wrote on Twitter.
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The Long March 5B rocket was launched April 29 from Hainan Island.
Defence Secretary Lloyd Austin has said the U.S. military has no plans to shoot the rocket segment down, but suggested that China had been negligent in letting it fall out of orbit.
The Long March launched last week was the second deployment of the 5B variant since its maiden flight in May past year.
USA experts are now predicting that the rocket debris "will make landfall or land in the ocean between 9:04 and 11:04 P.M. Eastern", reported CNN's Pamela Brown, noting that their calculations had Spain, Israel, Saudi Arabia, Australia and New Zealand all in the risk zone. In late April, authorities in the city of Shiyan, Hubei Province, issued a notice to people in the surrounding county to prepare for evacuation as parts were expected to land in the area.
It is one of the largest pieces of space debris to return to Earth, with experts estimating its dry mass to be around 18 to 22 tonnes.
Last year, debris from another Long March rocket fell on villages in the Ivory Coast, causing structural damage but no injuries or deaths.