European stocks fell more than 1% on Friday (January 29), tracking declines in Asian and U.S. equity markets.
That was off the back of concern around the retail trading frenzy that has gripped Wall Street this week.
The benchmark STOXX 600 index dropped 1.6% in morning trade.
And was on course to end the week with its worst decline since late October.
Germany's DAX also declined.
The U.S. stock market had already been looking overvalued after a stimulus-led rally last year.
But it's been jolted this week by steep gains in heavily shorted stocks, including Gamestop and AMC Entertainment.
Shares of videogame retailer GameStop and headphone maker Koss Corp doubled in early premarket trading on Friday.
Amateur traders returned a day after online brokerage apps, including Robinhood, imposed buying restrictions on the stocks.
Fears also remain for traders around the potential economic damage from a new strain of the virus in Europe.
It's been a busy week for earnings too and on Friday Sweden's Ericsson jumped 7.0% after reporting fourth-quarter core earnings ahead of market estimates.
It's benefited from strong sales of 5G equipment.
Bitcoin jumped as much as 14% to a two-week high. That after Tesla chief Elon Musk tagged the cryptocurrency in his Twitter biography.