(Adds second tsunami warning lifted)

By Ahmad Pathoni

JAKARTA, Sept 12 (Reuters) - A powerful earthquake of 8.2 magnitude struck Indonesia's Sumatra region on Wednesday, triggering tsunami warnings in the Indian Ocean, sparking panic in coastal areas across Southeast Asia and causing at least two deaths.

Indonesia issued two tsunami warnings, one after the first quake, and the second after a smaller tremor a few hours later in the same area.

However, the Indonesian warnings and most others in the region had been lifted by 1600 GMT.

An official at Indonesia's meteorological agency had said gauges measured a wave surge of 1 metre after the first quake.

Indonesian presidential spokesman Andi Mallarangeng told Reuters one person had died after being hit by debris in Bengkulu, a town in south Sumatra close to the quake.

"The emergency rescue system has mobilised and the president has ordered the military to help the rescue effort," he added.

Rustam Pakaya at Indonesia's health ministry crisis centre said later two people had died and nine were seriously hurt.

Some buildings in Padang, the capital of West Sumatra had collapsed, witnesses reported, while Metro TV said some buildings had caught fire.

Padang Mayor Fauzi Bahar said three people were trapped in a collapsed three-story office building.

A Reuters witness said residents of Padang fled for higher ground.

"The city is in complete chaos. Everyone is heading to higher ground, I saw one house collapsed to the ground. I'm trying to save my family," said the witness in Padang, the provincial capital of West Sumatra, north of the tremor's epicentre.

A huge earthquake struck the same area on Dec. 26, 2004, causing a massive tsunami and over 230,000 deaths in countries across the region.

Indonesia suffers frequent quakes, lying on an active seismic belt on part of the so-called Pacific "Ring of Fire".

Indonesia's meteorological agency said the big quake's epicentre was 159 km (99 miles) southwest of Bengkulu, a remote area of mountains and forests.

The Pacific Tsunami Warning Center issued an Indian Ocean tsunami warning after the first quake struck at 6:10 p.m. (1110 GMT). Authorities from Malaysia, Sri Lanka, Bangladesh and Australia issued independent warnings, as did India for the Andaman and Nicobar islands and France for the island of Reunion.

By 1600 GMT, tsunami alerts remained in place for Western Australia, Bangladesh and Reunion.

Some residents of Singapore, Malaysia and Thailand also felt the first quake and some buildings were evacuated.

(Additional reporting Harry Suhartono, Mita Valina Liem, Ed Davies)

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