Some of the heaviest rain to have fallen on Bangkok in two decades began on Tuesday evening and has overwhelmed the capital's main canals, making it difficult to drain the excess water from some parts of the city, said governor Chadchart Sittipunt on Wednesday.
Bang Khen district, for instance, reported 170 millimetres of precipitation since Tuesday -- the highest in 20 years.
As a result, water levels along Klong Lat Phrao and Klong Prem Prachakon, the district's main drainage canals, have also risen, causing floods in certain areas.
Some of the most affected locations include the Bang Khen roundabout and areas surrounding the tracks of a new electric train route, which the governor said was partly to blame for slow drainage.
He said run-off from Pathum Thani was compounding floods in the area.
The Bangkok Metropolitan Administration (BMA) and the Royal Irrigation Department (RID) are doing the best they can to drain the flood water off the city's streets, but high water levels across the city's main canals have made it difficult, said the governor.
With more rain expected today, the public has been advised to plan their trips accordingly.
Mr Chadchart urged motorists to keep an eye on the weather forecasts, as well as flood reports and traffic conditions.
"Insufficient planning has resulted in many motorists getting stranded in flooded areas," he said.
"With so many cars stuck in these areas, even military trucks deployed to help flood victims couldn't reach them in time.
"These lessons have been learned and we hope to make [our response] better," he said.
At least 17 locations in Bangkok were flooded from Tuesday night until Wednesday morning, according to the BMA's flood control and mitigation centre.
On Tuesday night, in particular, the floods paralysed traffic in certain parts of the city.
Mr Chadchart also expressed his gratitude to the RID for their help in handling the floods.
The governor said the department let the BMA use 21 of its water pumps to drain water from heavily flooded areas.
Residents living in Bang Khen, Lat Phrao, Don Muang, and Chatuchak are advised to remain vigilant as more heavy rain is on the way.
Gen Prawit Wongsuwon, the caretaker prime minister, in his capacity as chairman of the National Water Command Centre (NWCC) has instructed all agencies under the NWCC to fully support Bangkok and other provinces and ensure prompt flood response measures.