The police are searching factories where the drugs were being manufactured. (Representational)

In one of the biggest drug hauls in Mumbai, the Anti-Terrorism Squad seized 129 kg of mephedrone, worth over Rs 51 crore, a senior police official said on Tuesday.

"The drugs were seized on the intervening night of Monday and Tuesday," Deputy Commissioner of Police Vikram Deshmane told news agency PTI.

"We searched two people and recovered 9 kg of mephedrone. They led us to three more people from whom we seized 120 kg of the drug. The total value of the drug is Rs 51.6 crore," he added.

"Preliminary probe has revealed that the accused used advanced technology and high quality chemicals to produce mephedrone in large quantities. Search is continuing at the factories where the drugs were being manufactured," he said.