SEOUL—North Korea has begun to remove buildings from around its nuclear-test site in a step toward dismantling the facility, new satellite imagery shows, as the regime seeks to build trust with the U.S. after declaring its nuclear arsenal complete.

Roughly a week before the Punggye-ri site is set to host international journalists, images from San Francisco-based Planet Labs Inc., captured Monday, showed buildings gone and trucks working in the vicinity.

Pyongyang...