South Korea is to ban sales of some cars made by Porsche, BMW and Nissan, and fine the companies over $5 million as a probe into emissions documentation widens.

Seoul began investigating environmental certification on imported cars after Volkswagen last year admitted to installing emissions cheating software in some 11 million diesel vehicles worldwide.

The so-called defeat devices could detect when a vehicle was undergoing tests and lowered tailpipe fumes accordingly to make the cars seem less polluting than they were.

The South Korean government said Tuesday it had found certification errors in 10 models sold across the country -- two from Nissan, one BMW and seven Porsche -- and would slap a combined 6.5 billion won (US$5.6 million) fine on the firms.

"We will allow Nissan and BMW to clarify their positions through a hearing and file a legal complaint if irregularities are confirmed," Hong Dong-Kon, an environment ministry official in charge of auto environmental standards said.

Porsche already admitted its errors with the certification documents and has stopped selling four of the seven affected models, Hong said.

In August, the environment ministry banned the sale of 80 Volkswagen models and fined the company $16 million for forged documentation on engine noise levels, fuel efficiency and emissions.

The scandal has taken its toll on the company's reputation in the country, with its sales in South Korea plunging 33 percent in the first half of this year from a year earlier.

Foreign carmakers, especially German brands like Volkswagen, have steadily expanded their presence in the South's auto market long dominated by local giant Hyundai and its affiliate Kia.

Foreign cars accounted for about 15 percent of total auto sales last year, up from 10 percent in 2012.