Twin sisters Adrienne and Marienne Chew were about to step into their Upper Thomson Road home on a Friday night last November when they heard a shrill cry for help.

The 21-year-olds were shocked to see a young man in his 20s strangling their teenage neighbour.

"He looked like he was going to drag her into the house. I thought he was going to rape her," said older twin Marienne, who alerted her father, Mr Vincent Chew.

The 52-year-old scuba instructor quickly pinned the man down while his daughters called the police. In between gasps, the victim said the man had tried to rob her while she was walking home.

For their public spiritedness, Mr Chew and his daughters, both undergraduates, were among 85 citizens presented with a National Day Award yesterday at the Home Team National Day Observance Ceremony.

"The reason we can keep Singapore safe and secure, and our crime rates low, is because of people who come forward to help, sometimes to stop crime from being committed," said Home Affairs and Law Minister K. Shanmugam in his National Day Message before the ceremony.

He added that the community will play an even greater role when Prime Minister Lee Hsien Loong officially launches the national SGSecure counter-terrorism movement next month.

Mr Chew, whose family has lived in the Upper Thomson area for eight years, said: "The police can't be around all the time, so we were just doing our part to help others when something happens."

Mr Shanmugam also presented awards to 105 Home Team officers, 13 volunteers and four teams, including Singapore Civil Defence Force officers behind the community-led Save-A-Life initiative and myResponder mobile application.

Yesterday, Minister for Communications and Information and Minister-in-Charge of Muslim Affairs Yaacob Ibrahim joined staff and students from madrasahs at the Singapore Islamic Hub to commemorate the upcoming National Day, which falls on Aug 9.