Flooding in and around the US city of Houston has killed at least five people and prompted mass rescues, reports said.

With rain wreaking havoc in the Texas city -- the fourth most populous in the country -- Governor Greg Abbott declared a state of disaster in nine counties.

A flash flood watch for Houston will remain in effect until Wednesday morning, with more rain expected Tuesday, the city's Office of Emergency Management warned.

Rain came down at rates as high as four inches an hour on Monday, the Weather Channel reported, saying some residents were trapped in their homes and cars.

The Houston Chronicle quoted authorities as saying at least five people had lost their lives in the deluge, including a junior high school teacher.

Officials in Harris County said more than 1,200 high water rescues had been carried out, including nearly 900 within Houston city limits, the newspaper reported.

CNN broadcast footage of cars partially engulfed on roadways that had turned into swollen rivers.

In one scene, a man is seen scrambling out of his car and swimming to safety through murky water on a submerged roadway just shortly before his car sinks and disappears from view.

Houston International Airport experienced its second wettest day ever recorded on Monday, the National Weather Service for Houston/Galveston said on Twitter.