SINGAPORE - A shipment of 585kg of methylamphetamine, or "Ice", which Australian authorities found concealed in fridges, did not originate from Singapore.

The Singapore Customs and the Central Narcotics Bureau (CNB) said in a joint statement this is according to preliminary investigations into the March 30 bust by Australian authorities.

"(It) was passing through Singapore on its way to Australia. Investigations are ongoing," said the statement released on Saturday (April 13).

Australian authorities had earlier said the container with 11 commercial fridges was shipped from Singapore, but upon further query from The Straits Times clarified that it had "transited through" Singapore.

"Investigations into the origin of the illicit concealment remain ongoing," said a spokesman for the Australian Border Force (ABF), who declined to comment further on whether the shipment had gone through checks at Singapore ports.

Singapore authorities have also not commented on this.

The drugs were seized and a joint-investigation was launched by the Australian Federal Police, the New South Wales (NSW) Police Force's Organised Crime Squad and the ABF, following the bust.

Australian authorities estimated the more than half a tonne of drugs seized to be worth almost US$314 million (S$425 million).

The "Ice" was found hidden under the back panels of seven of the fridges, and Superintendent Garry Low of the ABF was quoted as saying that they were "a fairly crude import and disguised in a fairly basic manner".

The container was declared to contain electric ovens but when examined at Sydney's Container Examination Facility on March 30, officers found 11 commercial refrigerators inside. X-rays suggested there were inconsistencies with the make-up of the fridges, prompting officers to investigate further.

The drugs were found when the back panel of seven of the fridges were removed.

"(It's) the largest that's been seized in NSW this year and obviously one of the largest that's ever been seized," Supt Low was quoted as saying by Australian media.

Six days after the drug bust, Australian police conducted raids on commercial premises at Wetherill Park and a home at Edensor Park in Sydney.

During the searches, officers seized documents relevant to the investigation and electronic storage devices, said Australian authorities.