* June new home prices +0.7 pct m/m vs +0.7 pct in May

* Yearly growth in June +10.2 pct vs May's +10.4 pct

* Declining affordability raises housing market risk (Adds details on tightening measures and context on housing affordability)

By Yawen Chen and Ryan Woo

BEIJING, July 18 (Reuters) - Home prices in Beijing fell for the first time in more than two years in June, while Shanghai declined further and Shenzhen stalled, pointing to significant cooling in China's biggest real estate markets, official data showed on Tuesday.

Nationwide, home price growth slowed slightly last month as government restrictions to keep prices in check weighed on larger cities, though smaller cities maintained rapid growth due to less severe checks.

Big cities such as Beijing have acted swiftly this year to quell speculative property buying that have shattered price records and fuelled concerns about housing affordability.

Worries about growing household leverage have been joined by anxiety over China's addiction to debt, which authorities have been trying to curb over the past year in an effort to defuse financial risks.

The latest data suggests the real estate sector is cooling off at a moderate pace and is unlikely to suffer a steep correction as some had feared.

In June, average new home prices in China's 70 major cities rose 10.2 percent from a year earlier, decelerating from May's 10.4 percent gain, according to Reuters calculations based on data issued by the National Bureau of Statistics (NBS).

On a monthly basis, new home prices rose 0.7 percent in June, the same as the previous month's reading, the calculations showed.

"Sales declines in the biggest cities were quite significant, so prices are certainly not going to rebound," said Rosealea Yao, a property economist with Gavekal Dragonomics.

"The mild declining trend will continue through at least the first half of 2018," Yao said.

More than 45 cities, most of them top-tier cities with a sizable population, have imposed varying levels of restrictions since last October to curb fast-rising prices, with most of the latest measures introduced in late March.

The cooling effect is most visible in China's the biggest cities. Price growth in Shenzhen, Shanghai and Beijing slowed to 2.7 percent, 8.6 percent and 10.7 percent, respectively, from a year earlier.

From a month earlier, prices in Beijing fell 0.4 percent, marking the first fall since February 2015. Shanghai prices slipped by a further 0.2 percent, while Shenzhen prices remained unchanged.

DECLINING SALES

The value of new personal home mortgages in Beijing, Shanghai and Shenzhen in the first half of 2017 was equal to 30 percent of the total value of home loans in 2016, a Chinese state newspaper reported.