Eventually stretching some 65 kilometres (41 miles), the concrete wall will be accompanied by motion sensors designed to detect tunnel digging and is expected to be completed by mid-2019.
The project had been previously announced, but details of its construction had been kept secret until Thursday, when journalists were allowed to view aspects of it.
Workers -- local and from abroad -- have been labouring around the clock for nearly a year.
The barrier is being built on Israeli territory, east of the existing border fence, with four kilometres completed so far -- in the area of the town of Sderot, off the northern Gaza Strip , and the Nahal Oz area near Gaza City.
The technique used is similar to that for building support walls for high-rise buildings or underground parking lots.
On the Israeli side, only 74 people were killed, all but six of them soldiers.