Tropical Cyclone Mahasen began to lash the coast of Bangladesh with heavy rain Thursday, bringing the risk of flooding and landslides to densely populated, low-lying communities, CNN reports.At least four deaths have been reported, the state news agency said. Bangladeshi authorities relocated hundreds of thousands of people in vulnerable areas to safer ground ahead of the storm’s arrival.“The heaviest rains will fall on Bangladesh in the upcoming four to six hours,” CNN International meteorologist Ivan Cabrera said.The eye of the storm was expected to reach the country’s southeastern coast, near the city of Chittagong, later Thursday. But Cabrera said the wind and rain unleashed by Mahasen’s outer bands are likely to bring the worst conditions.The storm’s strongest gusts are forecast to reach 85 to 90 kilometers per hour (53 to 56 mph), weaker than the 120-kilometer-per-hour gusts of a hurricane.Authorities have suspended port activities at Chittagong, a major transport and commercial hub, and all domestic and international flights to and from the city’s airport have been canceled.The United Nations Office for the Coordination of Humanitarian Affairs (OCHA) warned earlier this week that Mahasen could put millions of people in the surrounding region at risk. Aid agencies and local authorities are scrambling to make sure residents are prepared and putting emergency supplies in position.“There is a flurry of activity going on both in Bangladesh and in Myanmar ahead of the storm,” Andreas Von Weissenberg of the International Federation of the Red Cross and Red Crescent said Wednesday. “It’s really a race against time in many ways.”Bangladeshi authorities relocated at least half a million people from the coastal districts of southeastern Bangladesh and are continuing to move many more, the top administrative officer of Chittagong Division, Muhammad Abdullah, said late Wednesday.He said that four and a half million people in eight districts of the division might be affected by the cyclone. Authorities have prepared thousands of buildings as cyclone shelters.The OCHA put the overall number of people ordered to relocate by the Bangladeshi government at one million nationwide.Bangladesh has learned to take a cautious approach to storms after the catastrophic impact of Cyclone Bhola in 1970 that is estimated to have killed 400,000 people, according to the OCHA. The country is regularly hit by lethal storms: Cyclone Sidr killed nearly 4,000 people in 2007, and about 200 people died in Cyclone Aila in 2009.