Bangladesh meteorological department issued warnings of 8 to 10-feet high waves as torrential rain and increasing wind speed signalled the advent of cyclone "Mahasen" here.
Around 200 cyclone centres have been set up across Bangladesh and thousands of residents in coastal areas evacuated following the grim forecast.
Airports at Chittagong and Cox Bazar have been shut. Ports in low-lying coastal areas have also been closed.
In Patuakhali, 110 medical teams have been readied and several control rooms set up.
Xinhua reported that cyclone "Mahasen" made landfall in Bangladesh's extreme southeastern Patuakhali district Thursday morning as a category 1 storm with top wind speeds of 100 kph, where authorities warned that the slow-moving storm could hit inland areas hard as well as coastlines.
Bangladesh Meteorological Department (BMD) reported "strong winds and a dangerous storm surge" along the coast after the storm came ashore at 7 a.m. A second landfall was expected by Thursday afternoon.
No casualties have been reported so far.
Authorities said the cyclonic storm started crossing the coast near Patuakhali at about 7 a.m.. The coast-grazing cyclone is likely to move northeastward further and may cross Chittagong-Cox's Bazar coast by noon of Thursday.
Bangladesh Wednesday ordered evacuation of about 1 million people from its coastlines.
Television footage showed widespread flooding in coastal areas of Cox's Bazaar, Chittagong and Patuakhali and 12 other districts where hundreds of thousands of people have also reportedly been evacuated from their homes.