Authorities have found three new illicit chemical dump sites in Melbourne’s northern suburbs, bringing the number of stockpiles uncovered in the past three months to nearly a dozen.

WorkSafe has identified three warehouses in Craigieburn suspected to contain large stores of chemical waste, a discovery made as part of an industry-wide investigation into a syndicate allegedly responsible for orchestrating one of the largest illicit dumping operations in Victoria's history.

Burnt-out chemical drums after the fire at the West Footscray factory last year. Credit:Justin McManus

Security guards have been camped out at the three warehouses since Friday night following a WorkSafe raid on the properties earlier in the day.

The sites are less than a kilometre from homes and about two kilometres from Merri Creek, which runs through most of the northern suburbs and feeds into the Yarra River.