Communities along the Chao Phraya River have been warned to stay on high alert for possible floods from Thursday until Sunday.

The period is when official expect northern flood run-off to reach Bangkok.

As of Tuesday, between 3,050 and 3,150 cubic metres of water per second were estimated to be flowing through Bang Sai district of Ayutthaya province.

That water is now heading for Bangkok, which could see water levels in the Chao Phraya River rise by another 30 centimetres to half a metre when coupled with the impact of a high tide, Bangkok governor Pol Gen Aswin Kwanmuang said.

The water level near the Pak Khlong Talat flower market in Bangkok was measured at 1.9 metres above the mean sea level early Tuesday morning. The water remains well below Bangkok's flood wall, he said.

Eleven riverfront communities that are home to 239 families in seven districts of Bangkok are strongly advised to closely monitor water levels in the Chao Phraya River.

The Bangkok Metropolitan Administration (BMA), meanwhile, is preparing to respond to flood emergencies along the flood wall stretching from Rama VII Bridge to Bang Na district, the governor said.

Sandbags are reinforcing areas where the floodwall is low or where gaps exist. Nearly one hundred stations are ready to begin draining water in case of overflows during a high tide, he said.