Authorities are looking into the private notebook of a lobbyist in an investigation into the conduct of about 60 officials that oversee urban construction and planning in Taiyuan city, capital of North China's Shanxi province, the Beijing News reported on Wednesday.

Provincial prosecutors said they are asking questions about officials from the Taiyuan urban planning bureau, including Wang Fengling, the deputy director of the bureau, Mei Gang, head of the construction management division, and Jin Xiaohui and Li Chenyi, two former deputy directors, according to the report.

Insiders said the corruption case has to do with real estate projects. Many owners of companies in that line of business have fled the city, the newspaper said.

Officials from the provincial publicity department and the Party discipline watchdog told China Daily they "had never heard about the case".

But an official from the urban planning bureau's general office, who only gave his surname, Huang, confirmed that both the deputy director Wang and the division head Mei have not returned to work for a long time.

"I haven't seen them in a while," he said without elaborating. "But everything in our bureau is going on as normal."

For about two years, the city's judiciary authorities and Party discipline watchdog have been investigating accusations of corruption leveled against local officials who have dealings in real estate.

Late last year, local prosecutors detained a person they consider to be a middleman, who they think gave bribes to officials on the behalf of developers.

Also taken into custody was the middleman's notebook, which contains records of bribes offered to more than 60 officials, the newspaper reported.