BEIJING (Reuters) - Home prices are still rising rapidly in most larger Chinese cities, but may have peaked in the high-flying southern city of Shenzhen, according to data giving the first insight into July price trends.

Prices of new homes in 100 cities rose 12.39 percent in July from a year ago, faster than the pace in June, research firm China Index Academy said.

The average home price was 12,009 yuan ($1,807) per square meter in July across the 100 cities, up 1.63 percent from the previous month, Index Academy said on Monday, compared with a 1.32 percent increase in June.

But in Shenzhen, where the cost of homes have risen the fastest in the country this year, prices peaked at 69,843 yuan ($10,509.03) per square meter in the first week of the month, then fell over 27 percent based on transactions later in the month, according to weekly data from property agent Centaline.

For the month of July, Shenzhen home prices fell 8.15 percent month-on-month, the fastest monthly decline since 2012, after hitting a record high in June, another agent, Midland Realty, said in a report.

Shenzhen is one of a number of top-tier cities including Shanghai which have tightened restrictions on home buying in recent months to cool price rises, which have sparked fears of asset bubbles.

But while prices in Shenzhen may have peaked, other first-tier cities continue to see strong year-on-year gains.

Prices in Shenzhen, Shanghai and Beijing rose 41.25 percent, 22.5 percent and 15.47 percent year-on-year in July, Index Academy said.

It is a different story in smaller cities, with 38 of 100 cities recording a decline in prices in July from year ago levels.

Chinese media has begun warning of risks in the rapid turnaround in the housing market this year, with calls for different real estate policies for different cities and concerns that speculative bubbles are forming.

The property market is a key driver of the world's second-largest economy and a robust recovery in home prices and sales gave a stronger-than-expected boost to activity in the first half of the year.

However, activity in the sector could turn if prices stall out or start to decline, especially with chronic overbuilding in many smaller cities, analysts say.

The China statistics bureau reports official housing price data on August 18.

(Reporting by Elias Glenn; Editing by Kim Coghill)