* Early warning indicators show "worrying" signs - BIS
* Credit-to-GDP gap points to risks in many countries
ZURICH, June 29 (Reuters) - Regulators should not dismiss "worrying" early signs of unsustainable property price and credit growth, which could leave borrowers vulnerable to interest rate rises or sharp downturns, the BIS said on Sunday.
The Bank for International Settlements, the global forum for central banks, said rock-bottom official interest rates, slashed to revive sluggish economies, have contributed to a boom in lending and real estate prices in some countries.
While the ECB has cut rates to record lows and decided to pump money into the euro zone economy, the U.S. Federal Reserve has hinted at interest rate hikes starting next year.
"Several early warning indicators signal that vulnerabilities have been building up in the financial systems of several countries," the BIS said in its annual report.
While no early warning indicator is completely reliable, dismissing such readings as inappropriate would be too easy, it said.
In many emerging market economies and Switzerland the credit-to-GDP gap, measuring the current ratio against its long-term trend, is "well above the threshold that indicates trouble", the Basel-based bank said.
The gap between real residential property prices and their long-term trend also suggests risks are accumulating in the housing sector, it said.
Swiss banks will tighten requirements for mortgage loans after repeated warnings from Switzerland's central bank and the International Monetary Fund that ultra-low interest rates, immigration and the country's safe-haven appeal for financial investors is feeding a property bubble.
Switzerland became the first country to activate a counter-cyclical capital buffer last year, forcing banks to hold extra capital against their mortgage books.
A combination of interest rate policy and macro-prudential tools would help countries tackle rising property prices more effectively than using just one approach, BIS chief economist Hyun Song Shin told Reuters in an interview.
Rising rates would push the debt service ratios - the share of income used to service debt - of several countries into critical territory, the BIS said, adding that borrowers in China were currently seen as most vulnerable.
Reporting by Alice Baghdjian; Editing by Ruth Pitchford