The rise was revealed in a survey of 2,250 people aged between 40 and 79 suffering from primary overactive bladder.

Yiu Ming-kwong, association chairman and a consultant at Princess Margaret Hospital, said 12.7 percent of the respondents are sufferers - a 2 percent rise compared with a study in 2006.

This should serve as a warning to people who regard frequent urination as simply a normal part of getting old.

"An overactive bladder can happen to anyone regardless of age and gender, although larger figures are spread among those aged over 40," Yiu said.

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One out of 10 to 20 people aged below 40 are sufferers while one in four were observed among those over 40.

Yiu said patients display frequent urination throughout the day, a sudden urgent need to urinate, and involuntary leakage or incontinence.

Another urologist, Chan Chi- kwok, said it is normal to urinate four to eight times a day, with overactive bladder patients going more than eight times.

The worst cases can see people rushing to the loo more than 15 times a day.

"Many people do not seek help from doctors since their lifestyles are not too disturbed by the illness," Chan said.

He warned that some overactive bladder cases were caused by early tumors. Overactive bladder patients are advised not to drink too much water.

One patient, surnamed Chiu, 47, has been suffering for 16 years.

"In the past, I went to the toilet every 15 minutes after drinking only one to two glasses of water. My situation improved after consulting the doctor and undergoing bladder training exercises," he said.

"Now I urinate around 15 times a day instead of more than 20. I still hope to make better progress."