(Dow Jones) Investors are funneling cash into exchange-traded funds that track emerging markets, pushing these volatile holdings toward year-to-date highs.

Two diversified choices for this sector, iShares MSCI Emerging Markets Index Fund (EEM) and Vanguard Emerging Markets ETF (VWO), are among the top five U.S. ETFs by assets.

"Investors have been pouring money into diversified emerging markets ETFs for the past three years or so, and that trend only appears to be gaining momentum," said Morningstar Inc. ETF strategist John Gabriel in a Sept. 14 report.

Nervous investors are fleeing U.S. stock funds and ETFs and seeking safety in bonds. However, international stock ETFs have quietly posted respectable inflows this year.

In August, for the second straight month, international stock ETFs led all asset classes in terms of net inflows, powered by strong demand for emerging markets funds, according to Morningstar.

"Over the trailing three-year period, emerging markets ETFs have accounted for more than 61% of all flows into international stock ETFs," Gabriel wrote.

Higher economic growth rates relative to developed markets and lower debt ratios in emerging markets economies have likely helped fuel the buying, he added.

In August, iShares MSCI Emerging Markets and Vanguard Emerging Markets ETF were the most popular ETFs as each raked in nearly $2 billion for the month.

From a performance perspective, the recent climb has brought the ETFs close to levels where rallies stalled earlier this year in January and April. If diversified emerging markets ETFs can climb free of resistance, it would be good news for the global economy. Some single-country ETFs have already broken out.

The recent surge of buying in emerging markets ETFs may reflect performance chasing. Emerging markets have jumped ahead of the S&P 500 Index (SPX) during the September rally. The iShares Emerging Markets ETF recently saw its 50-day moving average cross above the 200-day, which is often a bullish sign.