Residents of coastal regions of southeast India have been warned to prepare for a tropical cyclone which has been gaining strength in the Bay of Bengal.

A mass evacuation was under way in four districts of Andhra Pradesh and National Disaster Response Force teams are being deployed across the region.

Fishermen working along the coast of Andhra Pradesh have been advised to return to shore as the cyclone moves towards the area.

"Damage to thatched huts, breaking of tree branches, minor damage to power and communication lines are expected over south coastal Andhra Pradesh. Fishermen are advised not to venture out into sea," a government statement said.

National Disaster Mitigation Authority vice-chairman M Shashidhar Reddy told PTI: "We have asked the state government to ensure zero casualties. They have already started evacuating people living along the coastline to safer places."

Helen is expected to make landfall later today, bringing with her winds of over 90km/h and thunderstorms. According to NDTV, a storm surge of up to 1.5m is expected to hit the coast, meaning flooding is a risk in low-lying areas.

Cyclone Helen
Tropical cyclone Helen has led to a mass evacuation (NRL/NASA/ESA)

The cyclone was tracked off the coast of southwest Calcutta (Kolkata) on Wednesday and was moving westwards towards land.

Satellite data from the European Space Agency, Nasa and the Naval Research laboratory provided a comprehensive image of the storm, showing clouds over the open water of the Arabian sea, with rainfall occurring.

Helen was expected to intensify with winds reaching around 115km/h before hitting Andhra Pradesh near Chinnaganjam in southeastern India.

"Helen, which spreads over a geographical area of 300 to 400 sq km, is moving at a speed of 5 km/h. The speed will increase after the next 12 hours. The system would further intensify into a severe cyclonic storm during the next 24 hours," an expert told

"It would move west-northwest for some time, then west-southwest and cross south Andhra Pradesh coast between Nellore and Machillipatnam close to Ongole around morning of 22 November."

Experts said Helen would not be as severe as Cyclone Phailin, which hit Andhra Pradesh and Orissa in October and led to 500,000 people being evacuated. The cyclone also killed 45 people, with a number of fishermen getting caught in the storm.