JAKARTA (AFP) - Emergency teams headed to Indonesia's Sumatra island on Thursday after a massive 8.4 magnitude earthquake which shook the region and sowed concern as far away as East Africa.

Meanwhile a huge aftershock measuring 7.7 rattled Sumatra early Thursday, leading the Indonesian authorities to issue a third tsunami alert in 24 hours.

Two Hercules transport planes made a dawn assessment flight over the remote western city of Bengkulu, where collapsing buildings and trees claimed at least two victims.

With widespread damage and dozens reported injured, officials expected the death toll to rise. However fears of a catastrophic region-wide tsunami eased after alerts had initially been raised as far away as Kenya and Tanzania.

The Hercules planes were carrying an ambulance and other vehicles with medical teams and emergency relief also headed to the area, said Rustam Pakaya from the health ministry's crisis centre.

"We're also sending a full medical team from Jakarta including surgeons, a ton of medicine and four tons of food," the official told AFP.

"Three medical teams from the regional crisis centre in Palembang, South Sumatra, will leave early Thursday for Bengkulu," he added.

The huge earthquake hit at 1100 GMT on Wednesday, about 100 kilometres (60 miles) southwest of Bengkulu at a depth of roughly 30 kilometres, shaking office buildings across Southeast Asia.

In the capital Jakarta 600 kilometres further south, high-rise towers wobbled, water sloshed from swimming pools and panicked office workers ran into the streets. Elsewhere, power was knocked out and phone lines went dead.

The US Pacific Tsunami Warning Centre raised an alert for the entire Indian Ocean area including Indonesia, India, Sri Lanka, Thailand and the Maldives -- all affected by the devastating December 2004 Asian tsunami.

But Suhardjono, head of the earthquake division of Indonesia's meteorological agency, said tidal gauges off the Sumatran city of Padang had recorded an ocean surge of no more than half a metre (half a yard).

"There was definitely no damage caused by waves anywhere along the west coast of Sumatra," he told AFP.

Pakaya from the ministry of health's crisis centre said the confirmed toll was two and at least 11 people were injured. He could not confirm a report citing a Social Affairs ministry official saying seven were dead.

Dozens of people were injured in damaged buildings, said North Bengkulu district official Salamun Haris. The Bengkulu airport terminal was cracked but the runway was unaffected, another official said.

There were several reports that the damage did not at first seem severe.

"I saw some parts of houses crumbled to the ground but not huge damage. People ran out of their homes," Bengkulu resident Ayu Claudia said in a brief conversation before the phone lines went down late Wednesday.

Malaysia, Sri Lanka, the Maldives, India and Mauritius all issued separate tsunami warnings, while hundreds of thousands of people fled their homes in southern Bangladesh after a tsunami alert there.

The Kenyan government warned of a "massive" tsunami, before downgrading its alert. Tanzanian residents were urged to stay away from coastal areas.

Indonesia has endured repeated major quakes in recent years, including the 2004 quake that unleashed a tsunami across the Indian Ocean, killing more than 220,000 people in a dozen countries.

In May 2006, a quake rattled the country's main island of Java, killing more than 5,700 people and destroying some 300,000 homes. Two months later, another quake on Java killed more than 600.

In March yet another large quake hit Sumatra, killing more than 70 people, flattening buildings and displacing more than 1,700 people.

Indonesia, an archipelago of some 17,000 islands, sits on the so-called Pacific Ring of Fire, where continental plates meet -- and where earthquakes are a frequent and often deadly occurrence.

Any earthquake over magnitude 7.0 is considered to have the possibility for widespread damage and loss of life.