By Quentin Sommerville
BBC News, Shanghai
Another senior Shanghai official has been implicated in a major corruption scandal, a city spokesman said.
More than 100 investigators have been sent to Shanghai
The scandal has already led to the sacking of the financial hub's top politician, Chen Liangyu.
The investigation is being viewed as an attempt by President Hu Jintao to strengthen his position within the ruling Communist Party.
Sun Luyi is the latest senior party official to be investigated in Shanghai's widening corruption scandal.
The Party leadership in Beijing is wasting little time in stamping its authority on China's richest city.
1998: Beijing mayor Chen Xitong jailed for corruption
2000: Scores of officials implicated in smuggling scandal in Xiamen
2001: Mayor of Shenyang and his deputy sentenced to death for land deals
2006: Shanghai Party boss Chen Liangyu sacked over pension fund charges
Chen Liangyu, the Communist Party boss in Shanghai, was arrested on Monday on charges of misappropriating a large part of the city's pension fund and investing it in risky property ventures.
Sun Luyi, vice secretary-general of the Shanghai municipal committee, is accused of a severe breach of party discipline as part of the same inquiry.
Beijing has already sent over 100 investigators to Shanghai.
A state-run newspaper reported on Thursday that a separate team of investigators had examined the city's property rules and found them wanting.
Officials in Shanghai, including Mr Chen, are believed to have resisted Beijing's efforts to ease a bubble in the property market as part of efforts to cool the country's over-heating economy.
The sackings and the deepening investigation are widely viewed as an attempt by President Hu Jintao to weaken the political stronghold of his predecessor, Jiang Zemin, a former Shanghai mayor.
President Hu is taking on the so-called Shanghai faction in an attempt to strengthen his own position before an important party congress due to take place next year.