B747 Captain reported a fuel imbalance during climb. A fuel leak was confirmed visually and the flight crew performed an in flight shut down of the left engine and a diversion for a precautionary landing.

Narrative

During climb out in the low 30's; I noticed a 1100 lb fuel imbalance (left wing low). This was not the case on the ground. We had 28000 lbs on board at takeoff and should only have been burning fuel from the center tank. I observed the fuel quantity indicator for a couple of minutes and observed that the left wing fuel quantity was decreasing by 10 lbs every 1-2 seconds. I then asked our flight maintenance technician to do a visual inspection of the wing for fuel. He returned and reported that there was indeed significant fuel leaking from the engine pylon and upper wing surface. I went to look for myself and confirmed that there was a significant amount of fuel pouring from the upper surface of the engine pylon; an inspection panel just aft of the pylon; and from several seams in the upper wing also aft of the pylon. I returned to my duty station; contacted dispatch via Satcom; advised that we needed to make a precautionary landing. We agreed that ZZZ was best option. We ran the engine fuel leak QRH procedure; which necessitated a precautionary engine shut down and diversion. I advised ATC of the situation. We performed a single engine approach and landing at ZZZ. By the time we landed the amount of fuel lost was 1800 lbs from the left wing. I understand that a main fuel pump on that side had recently been replaced. Was a seal or sealant overlooked? The fuel leak stopped by the time we were on the ground. Was instruction Operating Evaluation Student (Captain) on doing a proper fuel check during climb and enroute when I noticed the imbalance. Reported situation to dispatch via Satcom; followed engine fuel leak QRH procedure; landed at ZZZ.