The derailment occurred at about 0550 hours, railway sources said, adding that rail traffic on the Arakkonam sector was disrupted and railways cancelled about seven trains and diverted some others.
The reason for the incident cannot be ascertained immediately, ADGP (Railways) R Sekar said, adding that the Safety Commissioner, who had left Bangalore for the spot, would go into the cause.
Minister of State for Railways K J Surya Prakash Reddy, who arrived here, announced a solatium of Rs two lakh to the next of kin of the dead, Rs 50,000 to those critically injured and Rs 10,000 for those with minor injuries. He later left for the accident site.
The Railways had pressed several buses into service to ferry stranded passengers and at least 200 continued their onward journey to Bangalore by the Guwahati Express.
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Southern Railway had cancelled several trains including Bangalore-bound Brindavan express, Duranto Express between Chennai-Coimbatore, Kovai Express, West Coast Express, Coimbatore Inter-City Express and Chennai-Tiruvananthapuram.
Mysore-Chennai Central Weekly Express, Chennai Central-Coimbatore Cheran Express, Chennai Central-Erode and Yeshvantpur-Muzaffarpur Express have also been cancelled, a Southern Railways release said.