* Hang Seng off 0.5 pct on big volume; down 1.8 pct on week
* Shanghai falls 0.5 pct, closes out best month in 15
* Financials drop on disappointing results
* AIA shares soar 17 percent on trading debut on demand (Updates to close)
By Vikram S.Subhedar and Farah Master
HONG KONG/SHANGHAI, Oct 29 (Reuters) - Hong Kong and Shanghai shares fell half a percent on Friday as financials slid on disappointing earnings, and as a strong debut for Asian insurer AIA cut demand for rivals' stocks.
Hong Kong's benchmark Hang Seng index <.HSI> fell 0.5 percent to close just below the key technical level of 23,100 points, sparking fears that its recent break above that level would not hold.
"Failed breakouts are to be shorted as those who bought on the breakout will be forced to sell to cut losses and will thus increase the selling pressure on the stock or the index." said the head of trading desk at a Japanese bank in Hong Kong.
AIA Group <1299.HK> surged 17 percent in its first day of trade as investors piled into the record offering in the world's hottest IPO market, chasing exposure to Asia's fast-growing life insurance business. [ID:nTOE69S06P]
But insurers overall were the biggest drag on the benchmark index after disappointing earnings from China Life <2628.HK> accelerated a shift of funds out of Chinese insurers into AIA. China Life fell 3 percent. [ID:nTOE69P02L]
Traders in Hong Kong said that AIA shares might find its way into some FTSE and MSCI benchmark indices earlier than expected, which would require index funds and exchange traded funds to buy into shares to adjust their portfolios accordingly.
Bank of Communications (BoComm) <3328.HK> shares slumped 7.8 percent, making it the top loser on the Hang Seng, after it boosted its provisions for potential bad loan losses, a spectre that is haunting many Chinese lenders despite strong profit growth. [ID:nLDE67H12V]
"It is the only major Chinese bank that reported a flat NPL ratio, while others have fallen. There is concern that (the NPL ratio) may climb later," said Paul Lee, an analyst at Tai Fook Securities.
The Hang Seng rose 3.3 percent in October although a weak market since mid-October ate into gains as investors preferred to pare back long bets ahead of the U.S. elections and the Federal Reserve policy meeting next week. [MKTS/GLOB]
On the week, the index shed 1.8 percent as investors took profits from its strong run-up since late August.
SHANGHAI DOWN, POSTS BEST MONTH IN 15
China's key stock index was weighed down by a selloff in brokerages such as Huatai Securities <601688.SS> which succumbed to profit-taking after recent gains.
The Shanghai Composite Index <.SSEC> closed at 2,978.8, after slipping 0.2 percent on Thursday. Though little changed on the week, the index has surged 12 percent this month, its biggest monthly gain since July 2009.
On a rolling 30-day basis, returns on the Shanghai Composite have this week outstripped the benchmark MSCI Asia Pacific ex-Japan index <.MIAPJ0000PUS> by the most since November 2009, according to Thomson Reuters data.
Analysts said uncertainty over the scale of an expected new round of quantitative easing by the Federal Reserve and the direction of the U.S. dollar have become a key focus for the Shanghai market, pushing the benchmark below the psychological 3,000 mark this week.
"This month the index has accumulated large gains so profit taking is very normal," said Zhang Qi, analyst at Haitong Securities in Shanghai.
Brokerages slumped after outperforming earlier this week as multi-year high trading volumes boosted their profit expectations.
Huatai Securities dropped 4.6 percent, while Haitong Securities <600837.SS>, which has gained nearly 40 percent this month, slid 4.5 percent. Top brokerage CITIC Securities <600030.SS> fell 4.9 percent.
Banks were also lower as BoComm's comments on non-performing loans pared appetite for the sector, despite strong results from its larger rivals earlier this week. [ID:nTOE69R09P]
BoComm shares in Shanghai <601328.SS> dropped 3.3 percent, while the world's most valuable lender, Industrial and Commercial Bank of China <601398.SS> fell 2.2 percent.
Analysts cited China's robust economic growth and solid third-quarter earnings as positive drivers for the stock market in coming weeks, but cautioned liquidity was key.
"In the medium term if more funds flow into the market, I am confident we can have a gradual good upward turn, but before this happens consolidation needs to take place," said Zhang.
(Editing by Kim Coghill)