A 6.6 earthquake off the coast of Indonesia's Sulawesi island sparked a tsunami alert and precautionary evacuations on Sunday, officials said.

Gorontalo province governor Fadel Muhammad told ElShinta radio he had ordered an evacuation of coastal areas after the strong earthquake rattled the northern half of the island at 3:22 pm (0722 GMT).

There were no reports of tsunamis 30 minutes after the earthquake 90 kilometres (56 miles) south of Gorontalo on Sulawesi's southern coast.

Officials said its depth 71 kilometres (44 miles) under the Tomini bay seabed probably ruled out a repeat of last week's killer waves.

On Monday, a 7.7-strength undersea temblor triggered a tsunami that lashed the south coast of Java island, killing at least 596 people.

Indonesia, which sits on the "Pacific Ring of Fire", where continental plates meet causing frequent seismic and volcanic activity, was the nation worst hit by the December 2004 Asian tsunami.

Some 168,000 people were killed in Aceh province when a 9.3-magnitude quake unleashed massive walls of water that reached 11 Indian Ocean nations, killing a total of 220,000.