More than 21,000 people have been evacuated in Johor after continuous rains, causing what officials say are the worst floods in years.

"So far 21,742 people have been evacuated from eight districts in Johor. There have been no casualties," Adnan Mohamad Yassin, an officer in the state's relief centre, told AFP .

"We always prepare ourselves to face the worst scenario during the monsoon season, but this year it is really bad, the worst in my experience," he said.

Adnan said a total of 126 villages with 4,767 families were affected by the northeastern monsoon rains, which had inundated villages, highways and residential areas in eight of Johor's nine districts.

Evacuees were placed in schools, town halls and even hotels, he said.

The worst-hit areas included the state's densely populated capital, Johor Bahru, and the central towns of Kluang and Muar.

Adnan said relief operations were being coordinated by the government's natural disaster department, and included rescue teams from the police, fire department, military and various humanitarian aid groups.

"The rain has stopped and the sun is shining in Johor Bahru right now, but the roads here are all submerged in water and traffic cannot move," Adnan said.

"We hope the water will recede soon so that people can go back to their homes. We have been told the rains could last for one week."

Human Resources Minister Fong Chan Onn appealed to employers to let workers take time off as the situation worsened, the state Bernama news agency reported.

"I hope that employers will grant leave to employees who can't make it to their workplaces, as this is an emergency situation. They must look after the well-being of the workers," Fong was quoted as saying.

"Let them take unrecorded leave or something, so that they can clean up their houses," he said.

Power lines down

Photographs of the scene showed villages and highways inundated with flood water while rescue teams and volunteers helped evacuate people from their homes.

People were also seen wading through waist-high flood water to reach shelter centres.

The News Straits Times cited government officials as saying the rains were a once-in-a-century phenomenon.

Dozens of villages, schools and residential areas in Johor Bahru were submerged, causing chaos and traffic congestion in and around the city.

The floods reportedly triggered minor landslides while the national rail company's south-bound services, including to neighbouring Singapore, have been suspended.

Phone and power lines were also downed by the flood waters.

More rain to come

"We have enough manpower, equipment and emergency funding for this purpose. There will also be enough food supplies for flood victims," Johor chief minister Abdul Ghani Othman told the daily.

Meteorological Services Department researcher Lim Si Fu said the monsoon rains were at their peak and were likely to continue for the next four to five days.

Central Selangor state which surrounds Kuala Lumpur could also be affected if the poor weather persisted, he told AFP .

On Tuesday alone parts of Johor recorded rainfall of up to 400mm, with an average of 350mm throughout the state where a reading above 200mm is deemed high.

"This year the amount of rainfall has been above average...it seems like the temperature in the tropics has been rising and this caused higher rainfall," Lim said.