A tsunami alert has been lifted around much of the Indian Ocean after an 8.6-magnitude earthquake struck off the western coast of Aceh, northern Sumatra, triggering panic as people fled for high ground.

The quake's centre was 20 miles beneath the ocean floor and about 308 miles from the provincial capital of Banda Aceh, according to the US Geological Survey (USGS). It was initially reported as being of 8.9 magnitude but was downgraded shortly after it hit. A 6.5-magnitude aftershock has since been reported.

Traffic jams were reported in Aceh, where people scrambled for higher ground as sirens mingled with sounds from the mosques, Reuters reported. A rescue team from Indonesia's disaster mitigation agency was sent to the region to help.

Officials in the neighbouring countries of Thailand, Malaysia and India issued precautionary evacuation orders along coastal regions. Thailand temporarily closed Phuket airport, according to local media, with warnings of waves up to 4 metres (13ft) in height hitting the holiday islands of Phuket and Krabi, although no tsunami waves have yet been reported.

Tremors, some lasting for as long as five minutes, were felt across south-east Asia after the earthquake hit. Reports on Twitter described employees rushing out of office buildings and families looking for safety as far away as Rangoon, Bangkok, Ho Chi Minh City, Singapore, India and Sri Lanka.

The Pacific Tsunami Warning Centre (PTWC) said an alert had been issued for 28 countries, including Indonesia, Bangladesh, Iran and Oman. An updated warning said sea-level readings indicated that a tsunami measuring 17cms (6.7ins) had been generated but that if no major waves had occurred "for at least two hours after the estimated arrival time, or damaging waves have not occurred for at least two hours, then local authorities can assume the threat is passed".

It warned, however, that damage to boats and coastal structures could continue, owing to rapid currents.

The PTWC lifted the tsunami warning for most areas of the Indian Ocean about four hours after the first quake.

Bruce Presgrave of the USGS told the BBC a destructive tsunami was less likely because the quake had been caused by the earth moving horizontally instead of vertically.

Indonesia sits above the ring of fire, a series of fault lines which make the archipelago nation of roughly 18,000 islands prone to volcanic and seismic activity.

The 9.1-magnitude quake that occurred on Boxing Day 2004 triggered a tsunami in the Indian Ocean that killed 230,000 people, nearly three-quarters of whom were in Aceh.

Esmer Golluoglu is a pseudonym for a journalist working in Rangoon