JAKARTA -- A series of moderate quakes shook the western coast of Indonesia's Sumatra island on Thursday, but there was no risk of a tsunami, the meteorology and geophysics agency here said.

Three moderate quakes hit Bengkulu province over a period of three hours early Thursday with the strongest, a 5.8-magnitude quake, striking at 5:22 a.m. (2222 GMT Wednesday), the agency said in a statement.

The strongest tremor struck at a depth of 20 kilometers (12 miles) under the seabed, 105 kilometers southwest of the city of Bengkulu. The US Geological Survey put the magnitude of the quake at 5.6.

There were no immediate reports of casualties or damage.

Two other quakes with magnitudes of 5.3 and 5.4 hit around the same location at 3:17 am and 6:23 am, respectively.

Indonesia was the nation worst hit by the quake-triggered Asian tsunami in December 2004, which killed 168,000 people in the country's Aceh province alone.

A 8.4-magnitude quake hit western Sumatra in September, killing 23 people. It was followed by a series of major aftershocks.

Indonesia sits on the so-called Pacific Ring of Fire, where continental plates meet -- and where earthquakes are a regular and often deadly occurrence.