Four men have been charged with importing almost $100 million worth of drugs, mainly heroin, into Sydney — making it one of the biggest busts of its kind in Australia.

Border Force officers found more than 150 kilograms of heroin stashed in wooden boxes sent on a flight from Malaysia to Sydney in January this year.

The crates were labelled as gym equipment and supplements, but instead, had 400 blocks of heroin hidden under a secret floor with straw hats sitting on top.

Organised crime squad investigators from NSW Police removed the contents and carried out a controlled delivery to an Airbnb rental property at Arncliffe in Sydney's south.

A 31-year-old man allegedly went to pick up the delivery Thursday before dispatching some of the drugs to two men, aged 23 and 29.

Detectives then arrested the 31-year-old at a house in Chippendale and the 23-year-old at a house in Strathfield in Sydney's inner-west.

The other two men were detained at Condell Park and Newcastle, north of Sydney.

Alleged drug syndicate headquarters in Burwood

One of four men charged over the drugs found in Sydney. ( Supplied: NSW Police )

After raiding the properties, officers then searched an apartment at Burwood — the headquarters of the alleged drug syndicate.

Police seized another 7.5 kilograms of heroin, more than $26 million of the drug ice, more than $200,000 in cash, drug-making equipment, mobile phones, computers, financial documents and knuckle dusters.

Detective Superintendent Tony Cooke took the opportunity to remind young people about the dangers of taking any sort of drug.

"This is a significant seizure — our young people these days will go the supermarket and buy all the great foods and then on Saturday, they'll be at a dance party popping a pill — they do not where it comes from or what's in it," he said.

"They're full of poison, people have died and people need to start to think about what it is they're doing — we really need to see some cultural change."

Three of the men have been charged with commercial drug supply, while the 31-year-old was charged with participating in a criminal group.

All four have been refused bail and if convicted of the charges, are likely to face lengthy jail terms.

Investigations are continuing and police expect to make further arrests.