It was EXTRA LARGE refinery flairs in Pair Gudang Johore, I personally saw it last night and took video and photos.
I actually saw if from CTE near AMK at first, big spectacular, and then, I purposely drove to check it out, I drove until Punggol, and then Seletar North near sea side and next to concrete plant.
A pair of twin flairs flame 20meters into sky, very loud, can be heard in Seletar.