An illegal taxi driver has been detained for using fake documents to pass off his vehicle as genuine, Shanghai traffic authorities said yesterday - the first time this charge has been used against "cloned cab" operators.

Previously, unlicensed cabbies faced lesser charges concerning illegal operations.

But now the authorities are keen to charge them with forging and using official certificates and seals.

This coincides with crackdowns on illegal taxis.

The cabbie, surnamed Wang, was stopped early on Thursday morning in downtown Hongkou District, police said.

Officers found that Wang was using fake taxi invoices, a fake license and even the electronic license tag - a recently introduced initiative - was found to be bogus.

"It's a former taxi, taken out of service in February," said an official with the traffic law enforcement team, who traced the vehicle to a local company.

Officials said illegal cabbies fool passengers into thinking they are using genuine cabs, and some then rob them.

Previously, illegal cabbies faced minor punishments and had their vehicles confiscated, said traffic authorities.

"Now we're trying to increase the penalty by charging them with forging official certificates and seals," said Chen Zhaohui, a traffic official.

Chen said the cabbies mainly get false licenses and vehicles fitted with cab lights and meters from underground markets.

Officials also admitted that many illegal operators are not being apprehended. Local commuters have recently reported being robbed by bogus taxi operators. City taxi watchdogs said they have received three reports of theft but suspect there are many more victims.

Passengers have been robbed of money, public transport cards and cell phones. Officials said they are still looking for the drivers.

Traffic police estimate that there are about 5,000 illegal taxis on city roads, compared to 50,000 legal ones.

Electronic tags have been introduced on licensed taxis to allow for instant identification.