A motorist was arrested for possession of an illegal drug yesterday after 16 grams of a substance suspected to be ketamine were seized from his car. It was the fourth such case in the city in the past three weeks. The 27-year-old man was arrested after he was found in a disoriented state in the driver's seat of a stationary vehicle in the eastbound middle lane of Kwai Chung Road, in Lai Chi Kok, shortly before 5am. Three packets containing a white powder, suspected to be ketamine, were found in the glove box, a police spokeswoman said. The man, who lives in Mong Kok, refused to go to hospital for treatment, she said. He was being held for questioning in Cheung Sha Wan police station, but no charge had been laid. Crime-squad officers from Sham Shui Po are investigating the case. The arrest came after Chief Superintendent Mike Demaid-Groves, of the traffic branch, on Thursday told regional heads to remind officers to keep a watch for drug-driving. Three taxi drivers were arrested in similar cases between December 23 and January 5 in Happy Valley, Kowloon Tong and Tuen Mun. Lai Man-kam, secretary of the Driving Instructors Association, urged police to boost enforcement to deal with drug-driving. 'Driving under the influence of drugs is very dangerous. It poses a danger not only to drivers, but also endangers the safety of other road users,' he said. Drug-driving is an offence under the Road Traffic Ordinance. Convicted drivers have their licence suspended for a minimum of three months and could face jail for up to three years and a fine of HK$25,000.