The Pacific Tsunami Warning Centre initially said the waves could reach Sri Lanka around 20.00 hours (8.00pm) Sri Lanka time but warned that actual times could be different.
A revised bulletin from the centre after a small wave hit the Padang island of Indonesia said destructive waves could occur along coastal lines.
The first wave could be small, and the second wave could come from five minutes to an hour later.
If no major wave is generated two hours after the estimated arrival time, local authorities could assume that the threat has passed, the Centre said.
"Danger to boats and coastal structures can continue for several hours due to rapid currents," the Centre said.
"As local conditions can cause a wide variation in tsunami wave action the all clear determination must be made by local authorities."
"Actual arrival times may diff