Chinese box office takings totaled 4.1 billion yuan ($640 million) in June, July and August, up 77% from the same period last year, with Hollywood pics dominating the market.

The results are the latest evidence of the boom in the Chinese biz, which saw some 115 million fans fill theaters, piquing the interest of Hollywood companies including Legendary and Relativity, which signed co-operation deals in recent weeks.

Last year, B.O. for the three months was $360 with auds of 68.2 million.

But the success of overseas movies will prompt further soul searching among Chinese regulators and orgs trying to protect and boost the local biz.

Of the 60 movies shown during the three months, five foreign films accounted for 70% of B.O. according to Entgroup, which compiles the data in China.

“Transformers: Dark of the Moon” was the best performing pic in the quarter, taking in $170 million, “Kung Fu Panda 2” took $69 million, and “Harry Potter and the Deathly Hallows: Part 2” took $64 million.

The best performing Chinese movie was “The Founding of a Party,” the propaganda epic about the birth of the Communist Party 90 years ago, with $63 million.

The Hollywood pics unspooled as part of the quota system operated by the government that allows roughly 20 foreign movies a year into China on a revenue-sharing basis.

The B.O. target for 2011, set out by the government’s official “Blue Book” cultural report on the entertainment industry, is set at $2 billion. It looks likely that a handful of U.S. films will account for most of this figure, increasing the pressure to make sure that local product is also strongly represented. Data from the State Administration of Radio, Film and Television showed that in the first half of the year, local films took in $450 million, up 38% over the same period last year, while foreign films grossed $430 million, up 1.6%, in the first six months.