An earthquake of 8.7 magnitude struck off the coast of Indonesia on Wednesday, sending residents there and in India dashing out of their homes and offices in fear. A tsunami warning was issued for the whole Indian Ocean.

The quake struck 308 miles (500 km) southwest of the city of Banda Aceh, on the northern tip of Sumatra island, at a depth of 20.5 miles (33 km), the US Geological survey said.

The quake was felt as far away as the Thai capital, Bangkok, and in southern India, residents said. Hundreds of office workers in the Indian cities of Bangalore and Chennai left their buildings, workers there said.

India's tsunami warning center said waves measuring up to 6 metres were expected along parts of its eastern coast. Smaller waves were expected to hit the remote Andaman and Nicobar islands. Sri Lanka also issued tsunami warning across the island nation's coasts.

The Pacific Tsunami Warning Center said a tsunami watch was in effect for the entire Indian Ocean.

Indonesia's disaster management agency said power was down in Aceh province and people were gathering on high ground as sirens warned of the danger.

"The electricity is down, there are traffic jams to access higher ground. Sirens and Koran recitals from mosques are everywhere," said Sutopo, spokesman for the agency.

The quake was in roughly in the same area as a December 26, 2004, quake of 9.1 magnitude, which sent huge tsunami waves crashing into Sumatra, where 170,000 people were killed, and across the Indian Ocean.

In all, the 2004 tsunami killed about 230,000 people in 13 Indian Ocean countries, including Thailand, Sri Lanka, India and Oman.

The 2004 quake was at a depth of 18 miles (30 km) along a fault line running under the Indian Ocean, off western Indonesia and up into the Bay of Bengal.

The quake was also felt in Sri Lanka and the southern Thai holiday island of Phuket, both of which were hit hard by the 2004 tsunami. 

Thai Meteorological Department deputy chief Somchai Baimoung said there was no tsunami warning yet in Thailand. Provincial officials along the Andaman Sea coast were preparing for possible evacuation if necessary.  

In Bangladesh, where two tremors were felt, authorities also said there appeared to be no threat of a tsunami.  - Reuters