The calendar year is only 8 months in but you wouldn't know if you looked at the growth of ETFs.

Assets stowed in ETFs have boomed in 2017, growing 35 percent to reach $4.8 trillion, according to London-based research firm ETFGI.

There are now more than 7,000 ETFs globally, coming from 331 providers in 56 countries.

Growth has continued in August, despite summer holidays in the northern hemisphere meaning it is usually a slow time of year for financial markets.

"August is typically a challenging month…with the average loss over the past 20 years for the S+P 500," said Deborah Fuhr, managing partner at ETFGI.

"This year the S+P 500 was up 0.31 percent in August and 11.93 percent year to date, Storms and political risks remain a focus for investors - the ability of the Trump administration to move forward on policy goals and hearings on Capitol Hill, Brexit negotiations, and North Korea is still an area of concern."

ETFs collected $42bn in inflows in August alone - clocking in the 43rd consecutive month of gains.

Equity ETFs took the lion's share of assets, taking in more than half of the monthly growth.

Fixed income ETFs came in second, gathering one-quarter of asset growth.

Always volatile commodity ETFs saw monthly inflows of $1.4bn, far less than equity and fixed income ETFs and "significantly less than the net inflows of $33.7bn gathered over the same period last year," ETFGI points out.

iShares was the biggest winner, taking in $13.7bn, followed closely by Vanguard with $10bn and Japanese asset manager Nomura with US$4.5bn.