So far, Thailand and Cambodia are the worst affected and the situation is expected to worsen as more rains, high tides and run-off from the north are predicted over the weekend, Xinhua reported Friday quoting the Office for the Coordination of Humanitarian Affairs (OCHA).
In Thailand, 2.4 million people in 26 provinces remained affected by the floods, and 12 provinces were on high alert for heavy rain and overflowing rivers.
This included the capital Bangkok, where the water level at the Chao Phraya river bank had increased to 2.1 metres from 1.9 metres, with the height of the river bank being at 2.5 metres.
One million people were also being affected in Cambodia, 250,000 in Vietnam, 490,000 in Laos, and four million in the Philippines.
Elisabeth Byrs, spokesperson for the OCHA, told media Friday that over half a million sq km were flooded in the region along the Mekong river, which originates in China and passes through Myanmar, Laos, Thailand, Cambodia and Vietnam.
It is considered the seventh longest river in Asia.