AHMEDABAD/MUMBAI - Four boys drowned in rough seas off the western Indian financial hub of Mumbai on Tuesday as India and Pakistan began evacuating people from coastal areas, two days before a cyclone is expected to make landfall.

Classified as a very severe cyclonic storm, Biparjoy is expected to land around Thursday evening between Mandvi in India's Gujarat province and Karachi in southern Pakistan.

Meteorologists predict maximum sustained wind speeds of 125-135 km (78-84 miles) per hour, gusting to 150 km (93 miles) per hour.

"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, south of Gujarat.

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

Eight districts in coastal Gujarat are expected to be affected, the state government said. Fishing has been suspended until Friday and 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.

A 1998 cyclone killed at least 4,000 people and caused hundreds of millions of dollars of damage in Gujarat.

Relief Commissioner Alok Kumar Pandey said that more than 20,500 people have been evacuated from coastal districts and the evacuation was expected to be completed by Tuesday evening.

In neighbouring Pakistan, paramilitary troops and local civil authorities also started moving people to shelters and relief camps, which were set up in schools and other government buildings, said Climate Change Minister Sherry Rehman.

Ships and boats have been moved from some areas of Pakistan's coast while hospitals in the region were put on high alert, added Rehman.

About 100,000 people will be evacuated by Wednesday morning, the chairman of Pakistan's National Disaster Management Authority said.

Two of India's largest ports, Kandla and Mundra, 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, 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.

(Reporting by Sumit Khanna in Ahmedabad, Rajendra Jadhav in Mumbai; additional reporting by Mohi Narayan; writing by Sudipto Ganguly; editing by Raju Gopalakrishnan and Nick Macfie)