The race at the Yongpyong Alpine Centre was moved to Thursday with an earlier start time to accommodate the men's downhill at the Jeongseon venue.
The downhill, the first scheduled event of the program, had also been moved to Thursday because of high winds at the Jeongseon mountain on Sunday.
The giant slalom had been much anticipated as the first in American Mikaela Shiffrin's bid for multiple gold medals in South Korea.
Ng, 16, the only Hong Kong competitor in Pyeongchang, will instead make her Olympic debut in tomorrow's slalom, where Shiffrin is the defending champion.
Shiffrin, 22, could realistically target four of five medals at the Games, but she will face stiff opposition from the likes of France's Tessa Worley, the reigning world giant slalom champion. German biathlete Laura Dahlmeier became the first double gold medallist of the Games by capturing the women's 10-kilometer pursuit. Dahlmeier, 24, won the 7.5-kilometer sprint on Sunday.