A suspected drug syndicate leader and three other men were arrested following an operation by the Central Narcotics Bureau (CNB) on Tuesday evening.
More than $103,000 worth of drugs were seized, including about 400g of Ice and ketamine, more than 900g of heroin, more than 800 Erimin-5 tablets and some 90 Ecstasy tablets.
Three digital weighing scales and improvised drug-smoking apparatus were also recovered.
On Tuesday evening, CNB officers observed a rider of a Malaysia-registered motorcycle entering a unit in Hamilton Road and leaving about 15 minutes later.
Officers tailed the 43-year-old Malaysian and intercepted his bike at the junction of Jalan Besar and Lavender Street, where they recovered Erimin-5 tablets and $6,000 cash after searching his bag.
Meanwhile, another group of CNB officers raided the Hamilton Road unit, where they arrested a 55-year-old Singaporean, believed to be the drug syndicate leader.
Later, officers also arrested a 37-year-old Singaporean, suspected of being an associate of the drug syndicate leader, and a 55-year-old Singaporean man, who is a suspected drug abuser.
The CNB said it takes a zero-tolerance stance on drugs and drug abuse, adding that it will take "strong action to ensure that drugs are kept off our streets".
Under the Misuse of Drugs Act, those found guilty of trafficking more than 15g of pure heroin will face the death penalty.
The amount, equivalent to 1,250 straws, is sufficient to feed the addiction of about 180 abusers for a week.