Residents of Sri Lankas' coastal regions rushed to safety after authorities issued the evacuation order following a strong earthquake off Indonesia which generated a tsunami.

"... the tsunami watch is cancelled for both main shock and aftershock," the Pacific Tsunami Warning Center in Hawaii said in an update.

It said some small tsunami waves had been reported off the eastern port of Trincomalee.

Hawaii's Pacific Tsunami Warning Centre has said an earthquake of 8.7 magnitude had occurred off the coast of Northern Sumatra in Indonesia Wednesday generating a tsunami but wave action monitored initially were around a foot in Indonesia.

It said that for any affected areas when no major waves have occurred for at least two hours after the estimated arrival time of damaging waves, then local authorities can assume the threat is passed.

Waves were initially estimated to hit around 4.00 pm in Sri Lanka's eastern and southern coasts.

But the Pacific Tsunami Warning Centre said danger to boats and coastal structures can continue for several hours due to rapid currents as local conditions can cause a wide variation in tsunami wave action.

It said the all clear determination must be made by local authorities.