Fearing a terrorist attack, several of them called the police.
A resident of Block 413, Ms Su, said she heard the first blast at about 10.45pm.
She went outside of her flat to take a look and saw that two teenagers at the rubbish chute area on the ground floor.
One of them put something that looked like a paper box in front of the rubbish chute area.
Then, both teenagers ran off.
Next, the paper box exploded, sending a loud blast around the estate.
That’s when a flurry of residents took a peek outside and got anxious.
Police officers who arrived at scene cordoned off the rubbish chute area and the open-air carpark next to it while SCDF officers checked on the remnants of the paper box.
The case has been classified as one of intentional alarm and is being investigated.