Police have charged two Polish men in connection with the seizure of 1.2 tonnes of drugs in Sydney — the biggest haul in the country this year.

The Australian Federal Police (AFP) seized the massive haul of MDMA, the equivalent of about 4 million tablets, during a raid on a storage facility in Hornsby, in Sydney's north.

The drugs, with an estimated street value of $145 million, were discovered in Sydney after a tip-off.

Two Polish nationals, aged 28 and 29, were arrested and have since been charged over the haul.

The seizure is the AFP's largest drug haul for 2016, and the fourth largest MDMA haul in Australian history.

About 1.2 tonnes of MDMA was smuggled into Australia concealed in these aluminium rolls. ( Twitter: AFP )

Border Force Commander Tim Fitzgerald said the drugs came from the Czech Republic and the syndicate went to extreme lengths to conceal them.

"The goods were declared as aluminium rolls and within the aluminium rolls there was a number of lead casings that concealed the actual narcotics themselves, so it's a very sophisticated concealment," he said.

"I'd suggest with this particular concealment and the nature of the use of lead it was meant to deter or disrupt our ability through the use of x-rays."

AFP acting deputy commissioner of operations Justine Saunders said there were still up to 88 aluminium rolls that the AFP had yet to examine, which could take another 24 to 48 hours.

She added that the seizure had international links and implications, and she expected more arrests would be made.

"If found guilty, the pair could face life in prison," she said.

"The sheer size of this seizure is a real concern and is certainly indicative of the drug culture in Australia today, the demand for illicit drugs continues to grow and the desire by organised crime to exploit the demand at the expense of our most precious assets, which is our youth, continues."

Ms Saunders said Australian police would be working with international and domestic partners to further dismantle the drug syndicate responsible for the haul, which was destined for the eastern seaboard.

Drug smugglers targeting Australian market

Commander Fitzgerald said there was a concerning increase in drug smuggling to Australia.

"In the last financial year alone the Australian Border Force intercepted over 18,000 individual detections at our borders," he said.

"That equates to 50 seizures of narcotics and precursors a day, so yes it is concerning."

Federal Justice Minister Michael Keenan said the raid was a reminder that drug syndicates from all over the world wanted to sell into the Australian market.

He said the Government was working to cut off demand for illicit drugs.

"If people are using drugs they are funding organised crime. And we want to give Australians who are in the midst of a drug addiction the opportunity to get off those drugs," Mr Keenan said.

"That's why we've invested $300 million — the largest extra investment in drug and alcohol rehabilitation in Australia's history."