Beijing has warned drivers that might consider violating Olympic traffic restrictions that they will be caught by a high-tech surveillance network, but offenders will receive only modest fines, local media reported on Monday.

In a bid to improve air quality and ease traffic on the Chinese capital's congested roads for the Games that start August 8, Beijing will ban cars on alternate days from July 20, depending on whether their license plates end in odd or even numbers.

Authorities had installed more than 10,000 "smart" devices, including cameras, "ultrasonic and microwave" scanners at regular intervals on major trunk roads and dozens of designated Olympic routes, the Beijing News said.

"They form a monitoring interface so that as soon as illegal cars hit the street, they will be discovered," the paper quoted a spokesman from the Beijing Traffic Management Bureau as saying.

Cars caught by the surveillance network would be fined 100 yuan ($15), the paper said, but it was not clear whether drivers could be fined multiple times in one day.

With more than 1,000 new cars hitting the street every day, Beijing is fast becoming one of the world's most congested cities. Officials hope that reduced emissions during the Games period will help improve air quality, although some athletes have lingering concerns.