Torrential rains in Malaysia have caused flooding that has driven more than 11,000 people from their homes, closed dozens of roads and disrupted shipping, authorities said on Saturday.

More than 66,000 personnel from the police, army and fire department have been mobilised nationwide to help rescue people stranded by flood waters and take them to shelters, Prime Minister Ismail Sabri Yaakob told a news conference late on Saturday.

Floods in Malaysia are common during the annual monsoon season between October and March, particularly on the country's eastern coast. But the downpour that started on Friday morning and continued into Saturday hit worst in the western state of Selangor - Malaysia's wealthiest and most populous region surrounding the capital Kuala Lumpur.

"It's a bit chaotic in Selangor right now... in other states, preparations would be made earlier for the monsoon. But in Selangor, this happened almost suddenly," Ismail Sabri said, adding that nearly 4,000 people in the state had been evacuated from their homes.

Authorities at Port Klang, the country's largest harbour, said shipping operations were severely disrupted by the floods. Dozens of highways and roads were also closed.

Videos posted on social media showed overflowing rivers, landslides, and cars submerged on abandoned streets.

Ashraf Noor Azam, a 26-year-old resident from the Selangor district of Shah Alam, said he had not expected the situation to be so serious and had been forced to leave his car on the side of a highway.

"After four hours stranded without help, and the flood isn't getting better, we decided to walk in the flood," he said in a tweet with a video showing three people walking.

Eight of the country's 16 states and federal territories saw water levels rising to dangerous levels on Saturday, according to a government website tracking flood developments.

The Meteorological Department warned that heavy rain in Selangor, Kuala Lumpur, and several states would continue until Sunday.