Unprecedented heavy rains in just five hours threw normal life in Chennai out of gear on Thursday forcing Tamil Nadu government to seek the army's help to cope with the calamity even as a cyclone threatened the state with further downpour.

As several areas of the metropolis went under water most of the people remained indoors but their woes are likely to continue as the met office has forecast more rains due to a deep depression in the Bay of Bengal.

The Chennai Corporation has advised people not to move out of their houses.

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Over 50,000 people in low-lying areas in north Chennai were evacuated and sheltered in corporation schools.

All educational institutions in Chennai, Kancheepuram and Tiruvallur districts were closed.

Many parts of the city went without power supply, which was cut as a precautionary measure to avoid any casualty due to electrocution.

More than 30 sub-stations were under knee-deep water and had been shutdown.

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Though there was no casualty due to rains in the city, the number of deaths due to heavy rains since the onset of monsoon on October 12 had gone up to 60, with four more deaths reported late on Wednesday, R Santhanam, State Relief Commissioner told PTI.

Relief work was in full swing, he said.

All train services from Chennai Central were cancelled till Friday noon with the railway track under waters. Public transport system came to a standstill with the gusty winds felling trees on the roads.

Though some international flights were diverted, domestic air services were maintained with some delay in arrivals and departures.

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Long distance trains from Egmore terminus was operated with some delay. There was also some disruption in suburban services in the Beach-Tambaram section.

Chief Minister J Jayalalithaa, who visited some flood-hit areas, said the army's help had been sought for draining the water and other relief operations.

Meanwhile, the weather office said the deep depression, which was 250 km east of Chennai, has moved westwards and lay centred about 150 km east of Chennai.

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The chief minister had deputed seven ministers and eight senior officers for overseeing the relief operations in the city and other ministers in the district.

The flood threat in the Cauvery had receded with inflows at Mettur dam coming down drastically to 76,000 cusecs today from 1.5 lakh cusecs.