By Sara Sjolin, MarketWatch

LONDON (MarketWatch) -- European stock markets ended a volatile day on a mostly upbeat note on Tuesday, with a global growth upgrade from the International Monetary Fund and a money-market intervention from the People's Bank of China helping markets.

The Stoxx Europe 600 index rose 0.1% to close at 335.76, after trading as high as 337.65 earlier in the day.

Among notable movers, shares of Unilever PLC (UL) gained 1.8% after the consumer-products company reported a rise in full-year earnings.

Shares of Novozymes AS (NVZMY) picked up 1.9% after the enzyme maker said it expects sales and profits to rise in 2014 from the previous year. It also posted a slightly stronger-than-expected profit increase for the fourth quarter and proposed a raised dividend for 2013.

On a more downbeat note, shares of Alstom SA tumbled 14%, making the company the worst performer on the Stoxx 600. Alstom said demand for its turbines has dropped off because global utilities are building fewer power plants and cut its operating margin forecast for the full year.

Shares of Royal DSM NV slid 10% after the life sciences company said it takes a prudent approach in 2014 and assumes a continued challenging macroeconomic environment with low growth in Europe.

More broadly, European indexes started to pare gains in late-afternoon action, mirroring the trading action in the U.S. There, the Dow Jones Industrial Average (DJI)turned negative as losses deepened for some of the companies reporting before the bell. Additionally, Goldman Sachs said U.S. stocks are starting to look overvalued, a view that was echoed in the Bank of America Merrill Lynch fund manager survey.

European markets had traded in positive territory at the open, tracking most Asian markets higher. The gains came after the People's Bank of China said it would intervene in the money markets and inject liquidity into commercial banks to cool the "squeeze in interbank-lending lending/borrowing rates, which had moved up in repose to the seasonal New Year cash drawdown by the public," according to Mike van Dulken, head of research at Accendo Markets. Around the holiday, large amounts of money are usually withdrawn from the banks to fund travel and gifts.

In Europe, the ZEW sentiment survey showed German economic expectations unexpectedly fell in January, although they remained at a high level.

Meanwhile, the International Monetary Fund lifted its global economic growth outlook for 2014 to 3.7% from an earlier estimate of 3.6%. The group also raised its forecast on the U.K. to 2.4% from 1.9% to reflect easier credit conditions and increased confidence in the country.

The U.K.'s FTSE 100 index , however, ended slightly lower at 6,834.26. Mining firms added pressure on the index as iron-ore prices fell to their lowest level in six months. The downturn was partly due to a retreat by Chinese buyers in response to slowing domestic steel production and rising stockpiles. Shares of Rio Tinto PLC (RIO) dropped 3.1%, Anglo American PLC lost 2.7%, BHP Billiton PLC (BHP) fell 1.7% and Glencore Xstrata PLC gave up 1.3%.

Germany's DAX 30 index rose 0.2% to 9,730.12. France's CAC 40 index was slightly higher at 4,323.87.

BNP Paribas SA climbed 1.9% in Paris after J.P. Morgan Cazenove lifted the French bank to overweight from neutral on expectations of "higher capital return and a sensible external strategy to unlock value."

Shares of Rémy Cointreau SA rebounded from earlier losses, rising 4.5%. The drinks maker said it doesn't expect sales to rebound in China during the crucial Lunar New Year holidays later in the month. The country's crackdown on official gift-making pushed sales down more than 20% in the latest quarter.

Outside the main indexes, shares of Nordea Bank AB (NRBAY) lost 1.5% after Credit Suisse cut the bank to neutral from outperform. The analysts said the stock had reached the fair-value level.

More must-reads from MarketWatch:

Get ready! Davos a-go-go and U.K. jobs drive Europe's week ahead

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Next cut in Fed bond buys looms

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