The epicenter of the tremor, which occurred at 3:34 am local time (0634 GMT), was 99 kilometers (61 miles) west southwest of the Chilean town of Talca and 117 kilometers (73 miles) north northeast from Concepcion, also in Chile, the US Geological Survey said.

There were no immediate reports of casualties or damage.

The survey had initially put the magnitude of the tremor at 8.5 but later adjusted it to 8.3. The location of the epicenter was also slightly corrected.

The US Pacific Tsunami warning center issued a tsunami warning for Chile and Peru, and a tsunami watch for Ecuador.

It said it was not yet known if a tsunami had been caused but "an earthquake of this size has the potential to generate a destructive tsunami that can strike coastlines within hours."

The center warned authorities to take "appropriate action".

The quake magnitude reading is based on the open-ended Moment Magnitude scale which is used by US seismologists and measures the area of the fault that ruptured and the total energy released.

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