Indian authorities ordered nearly 100,000 people to evacuate homes in Andhra Pradesh and Odisha, ahead of a severe cyclone the national weather office expects to make landfall by Wednesday.
Neighbouring Nepal and Sri Lanka have also issued weather warnings.
Cyclone Arnab is forecast to hit India's southwestern Andhra Pradesh coast as a "very severe cyclonic storm", with gusts of up to 150 kilometres (93 miles) per hour on Wednesday morning, the India Meteorological Department (IMD) said in a bulletin.
Torrential rain lashed the coast in the port city of Kakinda as heavy waves crashed on shore.
"I've never seen anything like this before," Kotesh Kumar, 35, told AFP, adding the government warned people to stock up on groceries.
"There was a cyclone here three years ago, but the water didn’t rise this much."
Cyclones, called hurricanes in the North Atlantic and typhoons in the Pacific, are a regular menace in the Bay of Bengal and northern Indian Ocean.
The storm season, however, has been turbocharged by the El Nino weather phenomenon that has caused unprecedented warming.
Neighbouring Sri Lanka, meanwhile, closed schools with warnings of torrential rain, with the island's Department of Meteorology warning storms could trigger flash floods and mudslides.
The military has been placed on alert, Colombo's Disaster Management Centre said.
Indian media reported that as many as 50,000 people have been told to move to safe areas in Andhra Pradesh, and 48,000 in Odisha.
- 'Damage' -
Nepal's disaster authority issued a warning on Tuesday, saying that as the storm travels inland towards the Himalayas -- likely overnight Thursday -- it will bring heavy rainfall as well as "a high risk of heavy snowfall, snowstorms and avalanches".
It called on tourists to avoid travelling to high mountain areas and advised those already there to remain in safe locations.
Nepal is still recovering from a catastrophic August 26 flood sparked by a glacial mountain collapse, which swept away more than 1,400 people and left over 5,000 missing.
India's weather bureau said it expects the cyclone to result in "total destruction" of thatched houses and create localised flooding, uprooting of power and communication poles, and "widespread damage" to standing crops.
In Kakinada, police barricaded roads leading to the sea.
Andhra Pradesh State Chief Minister Nara Chandrababu Naidu ordered the storm to be "constantly monitored and advance precautions taken", his office said in a statement on Monday.
"Adequate shelters and evacuation arrangements have been made," New Delhi's Cabinet Secretariat said in a statement.
The neighbouring Indian state of Odisha opened 1,735 cyclone shelters and imposed restrictions on movement in landslide-prone zone areas, the state's information office said.
Local media reported that Andhra Pradesh authorities ordered evacuations in key, low-lying areas and shut "all educational institutions" in some districts from Tuesday until Saturday.
Over 4,700 pregnant women residing in potentially dangerous sites were moved to hospitals, according to The Indian Express newspaper.