At least three people were killed and 45 injured when powerful earthquakes struck off the coast of Sumbawa island in central Indonesia, a health ministry official said on Monday.

Several buildings, including a health clinic, collapsed in the island's Bima district, said Rustam Pakaya, the head of the health ministry's crisis centre.

"The casualties are likely to increase and we are still assessing the situation," Pakaya told Reuters.

The quakes affected the eastern side of Sumbawa island, a rugged volcanic island that gets fewer tourists than neighboring Lombok and Bali.

The first quake of magnitude 6.7 struck 30 miles northwest of Raba in Sumbawa just after midnight, an official at the country's meteorology agency said.

A second quake of 6.8 struck about four hours later in the same area, triggering a brief tsunami warning, the official added.

The U.S. Pacific Tsunami Warning Center also said the quake could have produced a local tsunami no more than 100 km from the earthquake's epicenter.

The U.S. geological survey put the second quake at magnitude 6.3.

An earthquake measuring 6.0 also struck off the coast of Sumatra island in the early hours of Monday, some 100 km (60 miles) southwest of Mukomuko in Bengkulu, the local meteorology agency said. There was no tsunami warning.

On Sunday, a quake with a 6.2 magnitude hit the same area.

More than 20 people were killed when an 8.4 magnitude earthquake hit the Bengkulu area on September 12, damaging or destroying thousands of homes.

Indonesia, which is situated in a belt of intense seismic activity known as the "Pacific Ring of Fire," was hit by a huge earthquake in December 2004, triggering a devastating tsunami in the Indian Ocean, which killed more than 230,000 people in the region, including 170,000 Indonesians.

PHOTO CAPTION

Map locates magnitude 6.7 quake in the Sumbawa region, Indonesia. [AP]

Reuters