A 42-year-old woman was killed on Tuesday morning after she was hit by an SBS bus.

At about 7.35am, Madam Zhang Huirui, a housewife, was taking the pedestrian crossing across Clementi Avenue 3 when a double-decker bus running service route 78 knocked her down, pinning her underneath the bus.

She was dragged for about 5 metres before the bus came to a stop. Paramedics pronounced her dead on the scene at 7.50am.

The victim was the only person crossing on her side of the road. No one else was injured.

Mr Tan Ong Ah, 73, a retiree, was crossing the road from the opposite side when he witnessed the accident. He said: "The green pedestrian lights just came on. She started to cross but the driver just ran her over." He added that he heard a sickening sound when the bus hit her.

The police arrived at 8am to control the crowd and manage the traffic.

The victim's husband, Professor Gong Jiangbin, 41, was inconsolable when he reached the accident site at about 8.45am.

Prof Gong is an Associate Professor in the Department of Physics in the Faculty of Science at the National University of Singapore. The couple have a young daughter.

He collapsed in tears next to the victim's body, which was then already covered with a police tent. Paramedics had to escort him off the road for his safety.

Ms Pauline Tan, who lives a few blocks away, said that the junction is heavily used with " many buses turning from multiple directions". She added that many elderly residents also take the road to go to the market every morning.

The 47-year-old Singaporean driver was held by the police. He was distraught and would only speak with his wife, who reached the scene later.

Ms Tammy Tan, SBS Transit's senior vice-president for corporate communications, said the company was very sorry that the accident has happened and their priority is to render assistance to the deceased's family. She added that the bus captain has been suspended from driving duties with immediate effect until investigations are completed.