Singapore  - Fresh tremors were felt in Singapore Thursday as a second earthquake hit Indonesia's Sumatra island, 480 kilometres south-west of the city-state.

Shortly after the quake, which measured 7 on the Richter scale, Singapore authorities received about 60 calls from the public reporting tremors, police said in a statement.

"The public is advised that there is no cause for alarm," the statement said.

"Buildings in Singapore are designed to established building codes and are sufficiently robust to withstand tremors caused by distant earthquakes," it said.

On Wednesday, tremors were felt in 234 Singapore buildings when a magnitude-7.6 quake struck off Sumatra, killing at least 529 people. (dpa)