King and other base officials declined to provide any details on the cause of the lockdown.
About 5 a.m. MST Thursday, base spokeswoman Paula Thomas said the base had reopened to incoming personnel, and preparations were under way to allow people inside to leave.
She said there were no injuries resulting from the cause of the lockdown, which began about 5:30 p.m. She said more details would be released later in the day.
Thomas called as accurate media reports that about 1,200 to 1,400 people -- a mix of military personnel and contractors and civilian workers -- were inside the base when the lockdown occurred.
In his statement Wednesday, King said: "We are working as quickly and as thoroughly as possible to resolve a serious concern within the Test Area. ... Measures like these (lock down of our gates) are not taken lightly. No one is in immediate danger but these steps are required."
Military weapons are tested at Dugway, located about 85 miles southwest of Salt Lake City. Its primary mission is defending troops against biological and chemical attacks.
Encompassing more than 800,000 acres of Utah's west desert, the base also is used by the U.S. Army Reserves and the U.S. National Guard for maneuver training.