A 68-year-old woman was killed last Friday after being hit by a road sign that was dislodged by what was said to be a runaway bus.

Police said they were alerted to an accident involving a bus and a pedestrian at the junction of Bukit Panjang Ring Road and Bukit Panjang Road, at 9.56am.

Madam Ong Lim was taken conscious to the National University Hospital, where she was pronounced dead later, said Ms Agnes Chai, 26, one of Madam Ong's nine grandchildren.

Ms Chai believes her grandmother had been waiting for a taxi on the kerb after a visit to a market near her Cashew Road flat that morning, when a bus from funeral services firm Singapore Muslim Casket and Marble Contractor rolled down the slope, mounted the pavement and hit a road sign.

The road sign hit Madam Ong on the head, and also left her with a deep cut on her leg.

"My grandmother was a happy, jovial woman who was very close to her family... She would call my mother for a chat on the phone every day," said Ms Chai, whose mother is Madam Ong's eldest daughter.

"We are very shocked that this has happened."

A spokesman from the funeral services company said that its driver had parked the vehicle and ensured it was stationary before proceeding to a nearby mosque.

But Madam Ong's family is now calling for eyewitnesses or video footage to determine if a driver had been on board when the incident occurred.

The family has also lodged a police report on the matter.

Police confirmed that a report was made and that investigations are ongoing.