A fresh wave of violence rocked Nandigram on Friday as four police personnel were seriously injured in firing allegedly by members of the Trinamool Congress-backed Bhumi Uchhed Pratirodh Committee that is opposing the acquisition of farm land for industry.

This was the first major incident of violence in Nandigram since 14 people were killed in police firing there on March 14.

Police fired two rounds in the air to ward off attackers from Sonachura, close to Nandigram, but this proved futile and firing allegedly by BUPC members continued in two phases during the day, IGP (law and order) Raj Kanojia said in Kolkata.

District Enforcement Branch Inspector Prabhat Kumar was critically injured when he was hit by a bullet in the head. He was brought to state-run SSKM Hospital in Kolkata for surgery, Kanojia said.

Three other policemen sustained bullet injuries, he said.

"The firing was carried out from along a canal bordering Nandigram and Khejuri. The police outpost at Bhangabera was attacked twice -- first at 8 am and again at 1.30 pm," he said.

Home Secretary P R Roy said Nandigram was in the grip of violence since Friday morning and the situation there was reviewed by Chief Minister Buddhadev Bhattacharya and state police chief A B Vohra at the state secretariat Writers' Buildings.