Four boys drowned after venturing into rough seas in Mumbai as Indian authorities began evacuating people from western coastal areas on Tuesday, two days before a powerful cyclone approaches Gujarat state and neighbouring southern Pakistan.

Classified as a very severe cyclonic storm, Biparjoy is expected to make landfall around Thursday evening between Mandvi in India's Gujarat and Karachi in Pakistan with maximum sustained wind speed of 125-135 km (78-84 miles) per hour, gusting to 150 km (93 miles) per hour, the India Meteorological Department (IMD) said.

"Four boys drowned at Juhu beach on Monday evening. So far, we have found the bodies of two, and the search is still ongoing to locate the remaining two," said a police official in Mumbai, India's western metropolis that is south of Gujarat.

High waves in the Arabian Sea, accompanied by a heavy downpour and gusting winds pounded Gujarat's coastal areas, uprooting trees and resulting in wall collapse that killed three people in Kutch and Rajkot districts of the state, authorities said.

Eight districts in coastal Gujarat are expected to be affected, the state government said. Fishing operations in the region have been suspended till Friday while schools have declared holidays.

Gujarat is home to many offshore oil installations and major ports in the country and most have been forced to suspend operations.

According to the Gujarat government, 21 teams of the National Disaster Response Force and 13 teams of the State Disaster Response Force have been deployed in the state for rescue work.

"We have already started evacuations from coastal areas. More than 7,000 people have been evacuated so far and the number is expected to cross 50-60 thousand," said Kamal Dayani, a senior state official.

Two of India's largest ports - Kandla and Mundra - located in Gujarat, have suspended operations, the state government said. Other ports including Bedi, Navlakhi, Porbandar, Okha, Pipavav and Bhavnagar have also closed due to the cyclone, according to shipping sources.

Reliance Industries, which operates the world's largest refining complex in Gujarat's Jamnagar, declared a force majeure, suspending exports of diesel and other oil products from Gujarat's Sikka port due to the storm, traders said.

The Adani conglomerate's ports business, Adani Ports, said it suspended vessel operations on Monday at Mundra, India's biggest commercial port that has the country's largest coal import terminal, and also at Tuna port near Kandla.

The Indian Coast Guard said it evacuated 50 personnel from a jack-up oil rig off Gujarat's coast named Key Singapore, which is owned by Dubai-based Shelf Drilling and currently working for Cairn Oil & Gas (Vedanta Ltd), according to Shelf Drilling's website.

In Pakistan, the National Disaster Management Authority said instructions were being given to take precautionary measures in southern and southeastern parts that may be affected.