Bangkok authorities have declared a disaster zone across all 50 districts of the Thai capital after three consecutive days of heavy rainfall caused severe flooding throughout the city.

Governor Chadchart Sittipunt announced the disaster designation on Saturday, saying almost 300mm of rain had fallen since Thursday afternoon. The declaration gives local organisations the authority to take emergency action.

Nonstop rain inundated roads and canals, sending water into homes and businesses across the city. Photos and videos showed major roads submerged and cars abandoned after drivers were unable to move through the rising water.

Chadchart said the east of the city was the most severely affected and warned that further rain was forecast for Saturday. He added that flooding should recede once the rain subsides, as city officials work to drain floodwaters as quickly as possible.

"The rain keeps falling and we are doing our best. We are trying to pump the water out, but the water in canals are full," he said on social media. "The risk areas are those who live near canals. Every canal is now filled."

Later on Saturday, the government said the flooding situation had "stabilised" but warned it would still take two or three days for the water to drain, provided no further rain fell. "If more rainwater doesn't fall in the area, it will be solved," Chadchart said.

Residents were advised to move their vehicles to higher ground. Bangkok's public transport authority offered free access to MRT train park-and-ride car parks for vehicle storage until October 2.

Somkid Pheuk-ngam, 67, a vendor living near a canal just north of central Bangkok, said she had been forced to close her shop for two days.

"The water keeps coming in. It's hard to go out now. It's at my waist level," she told reporters. "I cannot go anywhere," she said, adding that the situation was "worse than the 2011 flood."

Widespread flooding across Thailand in 2011 killed more than 500 people and damaged millions of homes.

Reporting from a flooded street in the capital, a correspondent described the current situation as unlike typical monsoon downpours. "What usually happens is we get heavy downpours for a couple of hours, then you'll see the street often flooded but it would flow away into the drains quickly, and it would only happen in isolated areas too," the correspondent said.

"What's happening here is … happening all across the city. This is not a flash flood; this is persistent heavy rain since Thursday evening, and it shows no sign of letting up."

The Department of Disaster Prevention and Mitigation warned of low pressure across eastern, northeastern and central Thailand until Sunday, citing risks of flash floods, forest runoff, mudslides and river overflow.