The United States Geological Survey (usgs.gov) is reporting an initial quake strength of 8.7 Richter, with an epicentre about 500km southeast of Ambon Island.
AFP quotes Victor Sardina, a geophysicist with the US Pacific Tsunami Warning Center in Hawaii, as saying the tsunami generated was "not anywhere near" as large as the devastating tsunamis that struck Asia in 2004 or the one that hit Japan last year.
He said the tsunami measured a mere 35 centimeters (14 inches) near Padang, Indonesia, but could swell to as high as a meter (three feet) near Sri Lanka, adding that US scientists were still carefully monitoring the situation.
The Thai National Tsunami Warning Centre has confirmed that the wave, if it reaches Phuket - by no means a foregone conclusion - is likely to be less than 1.5 metres high.
Meanwhile, Phuket has just felt the effect of the first aftershock from the Sumatra quake, recorded at 6.5 Richter.
Phuket Traffic Police have urged all drivers to stop and stay where they are in order not to aggravate traffic chaos building up on the west coat of the island.
Phuket International Airport has been closed as a precautionary measure.
Readers are advised that a tsunami is not just one wave - it can be a succession of waves over a period of as little as five minutes or as much as an hour.
Please refresh this story periodically for updates.