* Both Asian bidders beat Australian offers
* Australian M&A double 2013
* Asian investors tapping mature, stable companies (Adds CKI-Envestra context, analyst and lawyer quotes)
SYDNEY, Aug 7 (Reuters) - Two of Asia's richest men won shareholder approval to buy Australian property and infrastructure firms for a combined A$4.5 billion on Thursday, extending the rush of offshore investors to tap the country's high-yield, low-risk assets.
Hong Kong billionaire Li Ka-shing's Cheung Kong Infrastructure Holdings Ltd (CKI) secured backing to buy Envestra Ltd for A$2.2 billion (US2.04 billion), from shareholders of the Adelaide gas pipeline owner.
Also ending a long bidding war, Singapore-listed property group Frasers Centrepoint Ltd, backed by Thai billionaire Charoen Sirivadhanabhakdi, scored shareholder approval to purchase Sydney residential developer Australand for A$2.6 billion.
Inbound M&A activity is booming in Australia as buyers in the Asia-Pacific region tap the country's array of well-established businesses in mature markets. Total transactions announced in Australia totalled $79 billion in the six months to June 30, compared with $45 billion in the first half last year, according to J.P. Morgan.
"It's quality assets in a good stable economic environment," said Rebecca Maslen-Stannage, a partner at law firm Herbert Smith Freehills in Australia who specialises in M&A.
"The fact that Australia has fared so well through quite difficult economic times means it's seen as a bit of a safe haven with safe government."
Australia-listed companies typically had diverse share registers making it easier to eke out a deal, Maslen-Stannage added, whereas "some of the companies you might find elsewhere in Asia where they're often dominated by one or two shareholders, if they're not willing to sell you can't shake out a transaction as easily".
In both deals cemented on Thursday, the Asian buyers beat out offers from domestic suitors which also held potential blocking stakes in the takeover targets.
Envestra's one-third shareholder, Australian Pipeline Ltd , had bid for Envestra, which had recommended the bid just as Li's firm made its higher offer. Australian Pipeline then waited until the day before CKI's offer closed to agree to it, prompting speculation it may make a last-minute counteroffer.
The Frasers offer nudged past the 50 percent acceptance it needed - it had 56.8 percent when the offer closed - without backing from Australand's biggest shareholder Stockland Corp Ltd , which has 19.9 percent.
Stockland since April has made two offers for Australand and was considered its most likely purchaser since Singapore's CapitaLand Ltd announced plans to sell what was a 59 percent stake in Australand in early 2013.
Its apparent refusal to support the Frasers offer also had stoked speculation it may launch a late counteroffer.
"Their acquisitions history has been very poor so at least they can say this is a win for them," CLSA property analyst John Kim said of Stockland, noting the Frasers A$4.48 offer price, 19 percent over its close on Feb. 10.
"We won't know until two years from now whether this would have been a good transaction for Stockland."
1 US dollar = 1.0796 Australian dollar Reporting by Byron Kaye; Editing by Michael Urquhart and Ryan Woo