A strong 6.4-magnitude earthquake struck off Aceh province in the north of the Indonesian island of Sumatra early Wednesday but there was no tsunami alert, seismologists said.

The shallow quake hit 10 kilometres (six miles) north of Reuleuet at 5:03 am local time (2203 GMT Tuesday), the US Geological Survey said. Aceh was devastated by the 2004 Indian Ocean tsunami.

In its initial assessment, the USGS said there was a low likelihood of casualties and damage.

In June a 6.5-magnitude quake struck off the west of Sumatra damaging scores of buildings and injuring eight people.

Indonesia experiences frequent seismic and volcanic activity due to its position on the Pacific "Ring of Fire", where tectonic plates collide.

Sumatra is particularly prone to quakes. Aceh province on the tip of the island was devastated by the quake-triggered tsunami in 2004 that killed more than 170,000 people in Indonesia and tens of thousands more in other countries around the Indian Ocean.