DHAKA, Bangladesh — A cyclone killed 242 people and left much of southern Bangladesh cut off from the rest of the country before heading inland and losing strength today, officials said.

Tropical Cyclone Sidr roared across the country's southwestern coast late Thursday with driving rain and high waves, spawning a 4-foot water surge that left low-lying areas and some offshore islands under water, according to Nahid Sultana, an official at a cyclone control room in the capital, Dhaka.

But by early today, the cyclone had weakened into a tropical storm and was moving across the country to the northeast, the department said, adding that while skies remained overcast, wind speed had fallen to 37 mph.

The cyclone flattened thousands of flimsy straw and mud huts, uprooted trees, electricity and telephone poles, and destroyed crops and fish farms in 15 coastal districts, local government officials and witnesses said.

The worst hit areas were communities in southern Bangladesh where most of the victims were killed by falling trees or debris from collapsing homes, while some drowned after falling off boats, Sultana said.

Much of the region remained without electricity and phone lines today, while blocked roads, rails and rivers left many areas cut off.

Power and communications in Dhaka were also down. Strong winds uprooted trees, snapped power and telephone lines, and sent billboards flying through the air, injuring several people, said Ashraful Zaman, another official at the cyclone control room.

At least 650,000 coastal villagers moved Thursday to cyclone shelters where they were given emergency rations, Ali Imam Majumder, a senior government official, told reporters in Dhaka.

Today, government and volunteer agencies dispatched relief and medical teams to the affected areas, where they had already sent dry foods, medicines, tents and blankets, he said.