Police in Perth believe they have smashed an international drug syndicate following the seizure of 12 kilograms of methylamphetamine with a street value estimated at $12 million.

They have also seized more than $400,000 in cash and casino chips.

Four men have been arrested over the haul.

Two of the men, 23 year-old Yik Chiu Wong and 24 year-old Yik Cheun Wong, are from Hong Kong.

The others are a 35 year-old Canadian national, Josip Petrusic, and Patrick James Preston, aged 41, from Sydney.

Police say all four were arrested while allegedly carrying four kilograms of the drug in Hay Street in Perth's CBD last Friday.

A search of a home in Stockdale Road, Kewdale, later uncovered another eight kilograms of the drug and $417,000 in cash and casino chips.

Superintendent Dene Leekong said it was the biggest methylamphetamine seizure for some time.

"This seizure is the biggest of its kind in Western Australia in the past five years," he said.

"Organised crime continues to target Perth to make millions from the sale of meth at the expense of the vulnerable in our community.

"This amount of drug represents about 120,000 individual hits, so dependent on what the individual street value purchase price is, that might represent up to $12 million."

Police said the group had been under surveillance since December and the decision was made to move on them last Friday during a "brazen" exchange of some of the drugs in broad daylight.

Superintendent Leekong said the methylamphetamine trade in WA appeared to be booming.

"The bulk of the drug we are seizing in Western Australia is meth," he said.

"I would say that organised crime are targeting Perth because it is a cash economy and it's highly profitable to sell meth by the kilo in Western Australia and make money at the expense of the vulnerable in our community."

All four men appeared in court on Saturday and have been remanded in custody to appear in court again at a later date.