B747-800 flight crew reported the aircraft inadvertently rolled 10 feet while parked on the ramp as a result of the chocks being removed prematurely.

Narrative

Upon arrival to the aircraft; I noticed only the nose wheel had chocks. When I told MX (Maintenance) about it; they were apologetic and said they would correct the issue. While doing the pre-departure briefing; 'doors closed & PARKING BRAKE SET;' we noticed the aircraft moving forward rapidly and gaining momentum. I immediately reached up and turned Number 4 Aux Pump on; which then pressurized the brake system and the aircraft came to a stop after moving about 10 ft. The headset from the ground had not been plugged in yet and luckily; no ground equipment was around the aircraft. After discussions through the inter phone with the ground crew; they had prematurely removed the chocks before there was any communications and before we could get clearance to pressurize hydraulics.Ground Crew inadequately chocking the aircraft; ground crew prematurely removing chocks before hydraulic system could be pressurized; and lack of communication with cockpit about their intentions. Using non standard procedures and making dangerous decisions regarding aircraft and personnel safety.I should have personally verified that additional chocks were brought to aircraft after we discussed the issue. But; there is no way of knowing how to prevent premature removal of chocks; especially when they had not even hooked up the ground headset for communication. They need more training or retraining emphasizing the danger to personal and equipment. This was a first in my career; especially how fast the aircraft started to move.