The projectile ricocheted into a passenger bus waiting at the barrier and into the border control booth, Moldovan broadcaster TV8 reported.
The border police officer sustained a minor injury, the agency said. The bus was at the barrier when the shell landed.
Moldova's Border Police links the incident to a Russian attack on Ukrainian infrastructure, TV Rain reported. The Palanca crossing operates on the Moldovan side of the border, opposite the Ukrainian checkpoint Mayaky-Udobne.