The Coast Guard aircraft hovered over the sea and its ships kept a vigil off nearby Idinthakarai as the villagers, including women and children, from Kudankulam and nearby fishing hamlets walked into the sea for the show of strength.
With black flags fluttering in the backdrop, the protesters said they were prepared to sacrifice their lives to protect their livelihood and ecology through the 'jal satyagraha', taking a leaf from a similar protest in Madhya Pradesh.
"What we are observing is Jal Sathyagraha – peaceful demonstration in the sea," said anti-nuclear activists who have taken the example of villagers of Khandwa district in Madhya Pradesh demanding land as compensation and reduction of Omkareshwar Dam recently.
Though the protest was intended to be from 10 am to 4 pm, the activists said they would continue it indefinitely on a relay basis.
Officials said Coast Guard aircraft and ships had been deployed to monitor the entire coastal area even as more than 4,000 police personnel, supported by Rapid Action Force, continued to maintain a strict vigil, having almost sealed the entire Kudankulam town to bar entry of outsiders.
Police said they were monitoring the human chain protest from a distance and would not act unless 'provoked extremely'.
The protest in the sea was held even as the Peoples Movement Against Nuclear Energy leader S P Udhayakumar, who has been spearheading the over a year-long stir, remained elusive with police searching for him.
Udayakumar had announced he would surrender before police on Tuesday night but later did a somersault citing people's sentiments against it.
"They (the people) are prepared to take any risk and even sacrifice their lives to protect their livelihood and ecology and the sea which provided them everything from any nuclear disaster," Amirtharaj Stephen of PMANE said, adding their protest would remain peaceful.
Meanwhile, police today served summons at the residence of Udayakumar in Kanyakumari district asking him to appear in a court in Valliyur near here in connection with the protest-related cases pending against him.
The protest against the KNPP turned violent on Monday that led to police firing resulting in the death of a fisherman in Tuticorin district and baton charge on the agitators here and house-to-house searches for PMANE activists.
Their demands included release of those arrested for agitating against nuclear power, compensation for those injured and whose articles went missing during police action, stopping fuel loading in the plant and no action against 'peaceful' protesters.
Fishermen of neighbouring Kanyakumari and Tuticorin districts held a protest condemning the police action on Monday and the killing of one person.