Authorities in Bangkok, Nonthaburi and Pathum Thani have been told to brace for possible flooding ahead of water discharge from the Chao Phraya Dam in Chai Nat before more heavy rain.

A monsoon trough is making its way down the country towards the Central Plains and upper South.

Provinces downstream of Chai Nat have been advised to prepare for a possible surge of water from the dam, which may cause floods in low-lying areas.

Prime Minister Prayut Chan-o-cha posted on his Facebook page that while heavy rains brought on by tropical depression Dianmu have begun to recede, the risk of flash floods and/or landslides remained high.

He said the Department of Disaster Prevention and Mitigation has been instructed to come up with a plan to deal with the nation's flooding issues.

The department was also instructed to send officials and equipment -- such as water pumps and rescue boats -- to help those affected by floods.

Intense showers will continue across the country until Thursday.

Chaiyaphum this week saw its worst flooding in 50 years.