HONG KONG, July 28 (Reuters) - Hong Kong private home prices were flat in June, official data showed on Wednesday, but realtors expect they will hit a new record high in the third quarter, supported by a recovering economy and hopes that mainland Chinese buyers will soon return.

The index of June home prices in one of the most expensive property markets in the world was unchanged at 394.5, compared to a revised 0.8% gain in May.

But, despite lingering COVID-19 pandemic fears, it just 0.6% lower than the all-time high of 396.9 in May 2019, before mass anti-government protests rocked the city.

"A persistent hot property market and improving pandemic situation is good for buying sentiment," said Thomas Lam, executive director of Knight Frank.

"If the border (with mainland China) can reopen by the end of year, some of the Chinese purchasing power will flood into Hong Kong,"

Realtor Centaline expected transaction volume in the secondary home market this month will ease slightly from June, but the total transaction value will remain above HK$40 billion ($5.14 billion) for the fifth consecutive month, the first time since 1997. ($1 = 7.7812 Hong Kong dollars) (Reporting by Clare Jim; Editing by Kim Coghill)