Thailand's record floods encroached deeper into the capital Friday, swamping a major intersection in the northern edge of the city centre and threatening the subway system.

The water from the country's worst flooding in more than half a century was filling Bangkok's Lad Phrao intersection, where three major roads meet.

Office towers, condominiums and a popular shopping mall are in the area, where local media say the water is 40 centimetres deep.

The intersection is just down the street from the famed Chatuchak Weekend Market, a key tourist attraction.

Three stations in Bangkok's subway system are being closely monitored but are still open.

Steel barriers have been put around the underground stations in recent weeks to protect against possible inundation.

The flooding, which started in the country's north in late July and has killed almost 450 people nationwide, has been spreading across Bangkok's north and west for more than a week.

The government has asked residents in eight of the city's 50 districts to evacuate.

Residents in several other districts have been warned that they should be ready to leave.

The water has yet to reach the city's central business district.