Calcutta, Sept. 17: Three young professionals working with an IT major in Calcutta were swept away by the sea in Mandarmani this afternoon just when low tide had set in -a risk-prone time for venturing into the water.

One person, Sumantra Banerjee, 30, has been found dead while a search stretched well into the night for Vinay Chaudhari, 28, and Lokesh Mehrotra, 36.

The search was extended late into the night because a high tide has been forecast for 2am on Sunday.

A fourth person, Javed Khan, was rescued by some residents who jumped into the sea.

According to police sources, Banerjee lived in Hiland Woods in New Town, Mehrotra is a resident of Salt Lake's EC block and Chaudhari of Meena Residency in Teghoria on the northern fringes of Calcutta.

The three, part of a group of 10 to 12 who reached the popular beachfront this afternoon, were apparently pulled away by the water that receded minutes after low tide set in. The incident occurred around 2.30pm.

"The low tide had just started to set in when seven or eight of the group went down to the sea. When the water recedes in the initial minutes after the low tide sets in, the force remains high. It seems the receding waters sucked the three men into the sea," a police officer said.

Swimmers are likely to experience stronger tugs away from the beach during low tide when the water drains away from the coastline than during high tide when the water moves over land, oceanographers said.

Scientists speculated on the basis of similar incidents in the past elsewhere along India's coastline that the swimmers swept away today may have been victims of what oceanographers call "rip currents" - strong, narrow channels of water moving outwards towards the sea.

"Rip currents occur when two off-shore currents moving in opposite directions converge, leading to narrow, fast-moving channels of water flowing away from the coast," said S. Prasanna Kumar, the head of physical oceanography at the National Institute of Oceanography (NIO), Goa. "Rip currents can be dangerous for inexperienced swimmers."

"The best way to escape a rip current is to swim parallel to the coast - to move out of the channel. It's not possible to directly swim against the rip current," said another NIO scientist, P.M. Muraleedharan.

It is not easy to delineate beach areas where rip currents are likely to occur because they are triggered by waves which are season-driven, Kumar said.

Indira Mukherjee, the sub-divisional police officer of Contai within which Mandarmani falls, said she was told people in the neighbourhood had asked the group to stay away from the sea then. "But the group didn't listen to them," said Mukherjee. This newspaper could not speak to any witnesses to corroborate the version.

Many boards have been placed on the beach warning tourists not to go beyond waist-deep water and avoid stepping into the sea when it is rough. Since it was full moon last night, the sea was rough through the day. Nuliahs, lifeguards hired by the local administration, had been warning tourists against getting into the sea today.

"But no one cares," said a police officer.

This was the second time in less than a month that tragedy had struck Calcuttans visiting Mandarmani. On August 21, three youths - all aged 21 and two studying in the UK - were killed in a collision between their Ford EcoSport and a BMW X3 on the long stretch of beach in Mandarmani that many revellers treat like a race track.

Mehrotra, the Salt Lake resident and IT professional, was accompanied by wife Pritha, according to the police. "He chatted with friends till 10.30pm on Friday.... They had set out for Mandarmani this morning," said a neighbour in Salt Lake this evening.

The group had gone to the beach around 2.30pm."The local people are well aware of the tide timings and know what is the right time to go into the sea. That's why they had asked the group not to go to the sea," said a police officer.

After speaking to other members of the group, the police came to know that they reached Mandarmani around 1pm. A police officer said they had put up in two separate hotels -- Massara Beach Resort and Diamond Glory. A fourth person, Javed Khan, was rescued by some residents who jumped into the sea after hearing the cries of those being swept away.Taken initially to a local hospital, Khan was referred to the Contai sub-divisional hospital for treatment.