The South China Post reported the man was also accused of sending images of children being sexually abused to a mobile phone belonging to a 10-year-old pupil after she attended his online Zoom class on Saturday.
The parent laid a complaint with the centre while the other mother contacted police.
When questioned by the centre's owner the man denied sending the X-rated content but refused to let his mobile phone be examined. He was fired immediately.
The South China Post said police arrested the man on suspicion of publishing child pornography – an offence that carried a maximum penalty of eight years in jail and a $360,000 fine in Hong Kong.
Police were now investigating whether there were more victims. The man's computer and mobile phone were now being examined.
Police had not yet laid charges, said the South China Post.