HONG KONG - Police are scouring the city for a gang of robbers who made off with 70 gold bars on Tuesday (Nov 22) morning.

The loot, worth an estimated HK$20 million (S$3.67 million), was snatched from a man who was unloading the bars off a delivery van outside the Heraeus Technology Centre in Fanling.

The South China Morning Post (SCMP), quoting a police source, reported that three robbers had approached the man before spraying an "unknown solution" into his eyes.

A witness said the trio shouted that they were armed with knives. They then disappeared into an alley with a trolley loaded with three bags.

The heist was over in about two or three minutes, according to the police source.

Each bag contained about 20 or 30 bars weighing roughly 1kg each.

The delivery van had contained nine bags worth about HK$60 million in total.

According to SCMP, the heist appeared to be an inside job as the robbers were aware of the time of the delivery and had planned an escape route.

Road blocks have been set up in the New Territories North region, while police officers have been alerted to look out for the robbers' getaway vehicle.

No arrests have been made so far.