HANOI, Vietnam >> A tropical storm whacked into Vietnam today, forcing 20,000 people to be evacuated, as the Philippines braced for a new typhoon and several Asian countries reeled under floods after some of the wildest weather this summer.

Prolonged monsoon flooding, typhoons and storms have wreaked untold havoc in the region, leaving more than 600 people dead or missing in India, Thailand, the Philippines, Japan, China, Pakistan and Vietnam in the last four months. In India alone, the damage is estimated to be worth $1 billion, with the worst-hit state of Orissa accounting for $726 million.

Several studies suggest an intensification of the Asian summer monsoon rainfall with increased atmospheric carbon dioxide concentrations, the state-run Indian Institute of Tropical Meteorology said. Still, it is not clear that this is entirely because of climate change, especially in India, it said.

After pummeling the Philippines and China this week, Typhoon Nesat was downgraded to a tropical storm just before churning into northern Vietnam on Friday afternoon with sustained wind speeds of up to 73 mph, according to the national weather forecasting center.

Heavy rains were reported in northern and central areas. Warnings were issued for flash floods and landslides in mountainous regions, and for flooding in low-lying areas. High winds whipped through the streets of the capital, Hanoi.

The storm had flooded streets across the southern Chinese island of Hainan on Thursday, forcing about 300,000 people to flee their homes, China’s official Xinhua News Agency said.

On Tuesday, Nesat bashed the Philippines, killing at least 43 people and leaving 30 others missing after causing one of the worst floods in decades in the capital, Manila.

The damage was estimated at $91 million, and preparations were already under way for Typhoon Nalgae, which was headed toward the northern Philippines. It’s expected to pack winds of 87 mph and gusts of 105 mph, gaining more strength before making landfall early Saturday and dumping heavy rains, forecasters said.

“The ground is still supersaturated and it cannot absorb more water,” said Graciano Yumul, the Philippines’ weather bureau chief. “This will just flow down to rivers and towns, and there is a big possibility that landslides, flash flooding and flooding could occur.”

At least four towns in the rice-growing province of Bulacan, north of Manila, remained submerged two days after Typhoon Nesat had moved on.

Thousands sought shelter on rooftops with no food, water and electricity, while a procession of other residents waded in chest-deep water down main roads to reach dry land.

“We have nowhere to go,” Celenia Espino of Calumpit township said from her home, which was filled with knee-deep murky water. “We have no means of transportation out of here.”

Disaster officials in Vietnam said fish and shrimp farmers were moved to safe areas along the northern coast. About 4,000 people, mostly the elderly, women and children, were also evacuated in three coastal districts in Nam Dinh province, said disaster official Tran Xuan Ngoc.

The storm comes on top of seasonal flooding in Vietnam’s southern Mekong Delta, where eight people were killed in four provinces this week, according to the national floods and storms control department. In addition, a woman and her grandchild were killed Thursday when their home was buried by a landslide in the northern province of Yen Bai, it said.

Other parts of Asia have not been spared either.

Two typhoons hit Japan this month, leaving at least 106 people dead or missing.

In Thailand, the disaster department said 188 people have been killed and three others remain missing after a series of tropical storms hit the country since late July. Nearly 2 million people have been affected by floods and mudslides, and 122 roads are impassable.

Heavy rains in Chiang Mai, Thailand’s second-biggest city, caused the Ping River to burst its banks and flooded the railway station, forcing a temporary shutdown in train service to northern Thailand. Meanwhile, 122 highways and roads nationwide are impassable.

More rainfall was forecast in northern Thailand for the weekend.

In the east Indian state of Orissa, monsoon flooding following severe drought earlier this year has killed at least 81 people since August, forcing hundreds of thousands to flee their homes. The state is asking for about $726 million in federal funds to help cope with the destruction.

India’s government says 18 million people have been affected by floods in northern Uttar Pradesh state, where 168 people have been killed since June and the damage is estimated to be worth $285 million. Flooding has also hit the eastern states of Bihar and West Bengal, and Assam in the northeast.

In Pakistan, monsoon rains since early August have flooded large parts of southern Sindh province, which is still recovering from extreme flooding from a year ago. The government says 7 million people have been affected.