JAKARTA/SINGAPORE (REUTERS, AFP, THE STAR/ASIA NEWS NETWORK) - An earthquake of magnitude 6.5 struck west of Indonesia's island of Sumatra on Sunday (Aug 13) but there was no tsunami risk, seismologists said as panicked residents fled their homes.

There were no immediate reports of casualties or damage in the quake, which hit at a depth of 35km at 10.08am (11.08am Singapore time), at a distance of 73km west of the city of Bengkulu, according to the United States Geological Survey.

"The earthquake was quite strong and shallow, it was felt all the way to Padang, West Sumatra, but there was no threat of a tsunami," Mochammad Riyadi, an official at Indonesia's meteorology and geophysics agency told AFP.

He said officials were checking if there were any casualties or damage.

Several Twitter users reported that they felt the tremors in Singapore.

When contacted, the Singapore Civil Defence Force said it received two calls about tremors, but there were no requests for any assistance.

The Straits Times understands the calls came from Sengkang and Tanjong Rhu.

Professor Kerry Sieh, director of the Earth Observatory of Singapore at the Nanyang Technological University, said the earthquake happened near the 8.4-magnitude quake that struck Sumatra in 2007.

With a magnitude of 6.5, the latest quake was milder. The 2007 quake would have had about 1,000 times the energy compared to the 6.5, said Prof Sieh.

He added that people who felt the tremors in Singapore would likely have felt them from the upper floors of tall buildings, which sway more during distant earthquakes compared to the lower floors of buildings.

Bengkulu resident Neng Hasnah said the quake felt very strong for a few seconds, forcing her and her family members to flee her house.

"I was carrying my seven-month old granddaughter and I had to run, all the neighbours also ran outside their homes," Hasnah told AFP.

Tremors were also detected in Johor Baru. Johor Fire and Rescue Department (Bomba) public relation officer Mohamad Riduan Akhyar said that occupants in two buildings felt the tremors at about 11am.

He added that the buildings were the Customs Tower in Tebrau and the Inland Revenue Board building in Tampoi, reported The Star.

"We received an emergency call over the incident at about 11.23am and officers were deployed to the areas.

"Both buildings were evacuated as a safety precaution," he said in a statement here on Sunday.

He said no injuries were reported.

Indonesia sits on the Pacific Ring of Fire where tectonic plates collide, causing frequent seismic and volcanic activity. An earthquake struck Indonesia's western Aceh province in December 2016, killing more than 100 people, injuring many more and leaving tens of thousands homeless.

Additional reporting by Audrey Tan