The city police arrested over 12 persons and seized 30 kg of ganja from them in three different places.
Following information, a special team mounted surveillance over a fish market at Pattalam and intercepted men who were travelling by an autorickshaw and a goods carrier at 3 a.m.
As they gave evasive replies, the police searched the autorickshaw and seized 25 kg ganja.
S. Panneerselvam, 38, Ganesh alias Purushothaman, 35, of Pulianthope and three of their associates were arrested.
Meanwhile, Adambakkam police arrested four persons with 4 kg ganja during night rounds.
Fishing Harbour police arrested three persons and recovered 1 kg ganja from them.