A severe cyclone was expected to hit Myanmar's main city Yangon later on Friday after the storm missed neighbouring Bangladesh, meteorologists said.
Severe cyclone Nargis had already hit outlying coastal regions and was packing winds of 120 to 150 miles (192 to 240 kilometres) per hour, Tun Lwin, director general of the meteorological department in Yangon, told AFP.
The storm was centred about 210 kilometres west of Haing Gyi island at the mouth of the Ayeyawaddy (Irrawaddy) river, or about 430 kilometres southwest of Yangon.
"It started to hit Ayeyawaddy Division since this morning. It will hit Ayeyawaddy, Yangon and Bago Divisions later on Friday. The tide could be increased by 10 to 12 feet (three to 3.5 metres)," he said.
Myanmar's state-run newspapers have run warnings about the impending storm.
Haing Gyi island could not be contacted for further information after it was hit.
The meteorological department said it was not yet known whether the storm had caused any damage or casualties.
In Bangladesh, fishing crews have been been told to stay close to the shore and not to venture into the Bay of Bengal,
after fears it would slam into the southeast coast.
But government forecaster Ayesha Khatun said the disaster-prone country was likely to escape the impact of Nargis.
"It is not going to hit Bangladesh. It will hit Myanmar later today, although the southern tip of Bangladesh could be affected," she said.
Bangladesh is still picking up the pieces after last November's devastating cyclone Sidr which smashed into the southern coast, killing more than 3,000 people.
Half a million people perished in Bangladesh in a cyclone in 1970. Some 138,000 died in 1991 in a tidal wave caused by a cyclone.