He said the investigation led to a "suspicious facility" at West Ryde in Sydney, where the arrivals of "suspicious containers" were monitored over several months, the ABC reports.
The drugs were found in a chemical shipment from Shenjing in southern China on February 22, and the men were arrested yesterday while allegedly trying to collect the drugs.
"The investigation remains ongoing and we've not ruled out further arrests either here in Australia or overseas,'' Mr Negus told a media conference this morning.
"We've already been in contact with authorities in China and a range of further inquiries are under way."
Federal Police say the massive drugs haul is the largest single seizure of P in Australia, with the previous record of 300kg in July last year.
"When the police and the community work together, these are the sort of results you get," NSW Police Commissioner Andrew Scipione said.
"We're very fortunate that somebody took the time to make that phone call.
"Make no mistake. This is a hideous, insidious drug.
"This is the sort of drug that sends people mad."
The three men are due to appear in Sydney Local Court today.
