Superintendent Ronnie Naidoo said on Tuesday a large number of vehicles were being brought into the country under false pretences.
"Unscrupulous dealers are acquiring these vehicles and importing them on the pretext that these vehicles are in transit and destined for neighbouring countries that do not prohibit the importation of second-hand vehicles," said Naidoo.
The number of illegally imported vehicles had risen over the years.
"In 1994, about 15 cases of illegally imported cars were reported. At the moment the number has risen from 15 to about 20 000 vehicles a year."
Sometimes the cars remained in the country or were sent to other countries where they were registered and brought back to South Africa.
"These vehicles are then registered in South Africa and sold to unsuspecting buyers," said Naidoo.
Most of the cars - which had been imported without the International Trade and Administration Commission (Itac) permit - were being imported from Japan, Europe and Singapore.
The vehicles also did not conform to safety and roadworthy requirements.
"They are usually not roadworthy in the country of origin and spares are difficult to obtain."
Although the vehicles were imported illegally, some of them would be allowed into the country under strict circumstances.
"Some of the documents required for this are import permits, an SARS customs bill of entry form, as well as an SABS letter of authority showing that the vehicle conformed to the country's safety standards," said Naidoo.
No one had been arrested in connection with the imported vehicles.
"No one has been arrested because its usually the victims(motorists) who are found in possession of these vehicles. So the cars get impounded," he said.
"The SAPS recommends that if you are intending to purchase a second-hand vehicle and there is uncertainty of the vehicle's origin, please verify this by checking with the International Vehicle Identification Desk on 012-365-9540," said Naidoo.