The mishap occurred on Shandy Road in Pallavaram, a busy market place here.
"A man who tried to stop the lorry by waving to its driver was first hit, followed by the two-wheeler in which four were on including a two and a half year old child," Police Inspector (Chromepet Range Traffic Investigation) Govindaraj told PTI.
He said the tanker driver was coming on the wrong side of the road.
The dead included a man, his child besides his wife and mother who were on the motorbike.
"The driver has been arrested, case has been filed against him and he will be remanded soon."
Locals said fatal mishaps had been on the rise in the area and neighbourhood.