SEOUL, April 22 (UPI) -- Activities at North Korea's Punggye-ri nuclear site are showing Pyongyang is getting ready for its fifth nuclear test, which could happen as early as Saturday.
U.S. and South Korea military surveillance captured the movements showing all preparations are complete, local television network SBS reported.
Satellite imagery showed a significant number of vehicles along with other equipment were no longer visible on site.
That could mean North Korea has taken the final steps before conducting its next test. All personnel have been evacuated to safe areas, according to SBS.
U.S. and South Korean military also have evidence North Korea's army has blocked roads around the area, in Kilju, North Hamgyong Province. The blockade also occurred immediately before North Korea conducted its fourth nuclear test on Jan. 6.
The U.S.-South Korea Combined Forces Command and Joint Chiefs of Staff are on emergency standby.
In light of recent North Korea announcements, it's likely the weapon being tested is a miniaturized nuclear warhead that can be fitted on a ballistic missile, South Korea press reported.
The test is taking place ahead of Pyongyang's Seventh Party Congress.
The last test in January, however, had an impact on the environment, according to a study from Germany's Federal Institute for Geosciences and Natural Resources, South Korean newspaper Donga Ilbo reported.
The earth's surface sank nearly three inches in some areas after the test, according to data collected from the Sentinel 1-a, a European satellite.
Interferometry was used to sense surface movements at the Punggye-ri nuclear site, and the scientists compared images from before the test, on Jan. 1 to images captured on Jan. 12.