China's stock of unsold new vehicles has hit a four-year high, due to increased production at a time of slowing demand, state media reported Tuesday.

The number of unsold new vehicles had risen to 170,000 as of the end of June, the highest level since it hit 200,000 in June 2004, the Shanghai Securities News said.

Sales in China rose 19 percent to 5.2 million units in the first half of 2008, slowing from 23 percent growth in the same period a year earlier, the report said, citing the National Development and Reform Commission's chief auto analyst Cheng Xiaodong.

The newspaper said automakers appeared to have been overly ambitious in expanding their production capacity while misjudging public demand.