Hong Kong and mainland authorities believe they have cracked a syndicate that smuggled electronic goods into Shenzhen through underground drains three times a week. Two Hong Kong men and four mainlanders were arrested and HK$600,000 worth of electronic goods were seized in the operation. One man was arrested when officers interrupted smuggling at the border fence in Man Kam To at about 12.30am on Tuesday. At the same time, mainland officers arrested five men and seized HK$1.2 million of smuggled goods found in the underground drainage system in Shenzhen. Customs divisional commander Lam Chun-keung said investigation of the gang, believed to have been operating for a month, began 10 days ago on the basis of intelligence. The smugglers removed the grating of a 45cm manhole near Tsung Yuen Ha and sent cartons of goods under the border fence through the 10-metre-long drain, drawn by ropes. Mainland smugglers in camouflage sneaked into the city through Shenzhen's drainage system, crossed the Sham Chun River and walked 500 metres through dense bush to reach the drain exit, where they pulled the goods through with ropes and carried them away in backpacks. Mr Lam said they took less than two hours to complete three round trips, smuggling more than HK$1 million worth of electronic goods into Shenzhen in one night. Chief Inspector Chim Fuk-hoi, assistant Ta Kwu Ling divisional commander for operations, said police would step up patrols of the 35km border fence.