A strong earthquake of magnitude 6.3 shook Indonesia's Sumatra island on Tuesday and was felt in Singapore and Malaysia as well, causing the evacuation of several buildings over 400km away.

There were no immediate reports of casualties or serious damage.

In the West Sumatra provincial capital of Padang, the quake sparked panic among seaside residents who feared it might trigger a tsunami.

However, there was no immediate warning of a tsunami from the quake, which had an epicentre under land.

The United States Geological Survey put its strength at 6.3 and said its epicentre was around 420 km (260 miles) from Singapore. The Indonesian national quake centre measured the quake at 5.8 on the Richter scale.

"It was really strong. I panicked, I ran out of the house just like the other neighbours," housewife Asmiarti, whose home is on the northern Padang shore, said.

"When we got out, our bodies were still shaking and the trees were also shaking. We fear there would be a tsunami but there has been no announcement so far."

Padang is one of the few Indonesian cities where a tsunami warning system is in place.

A witness said residents tried to reach higher places and their vehicles crowded main streets in Padang, triggering congested traffic across the city.

Callers told a Jakarta-based radio station that residents in several West Sumatra towns ran out of their houses when the quake was first felt, including some who said the quake knocked off roof tiles.

Tall buildings in Singapore's business district swayed slightly, occupants said, and the tremor was also felt in other parts of the island.

Traders said there was little or no impact on financial markets trading.

The tremor was also felt in west coast areas of Malaysia, the meteorological office in that country said.