* FTSEurofirst 300 has worst 1-day fall since Nov 2011.
* Chinese flash PMIs increase concern over state of economy
* Greek shares fall after PM resigns before new election
* Vopak slumps on concerns over its outlook
By Alistair Smout
LONDON, Aug 21 (Reuters) - European shares suffered their worst one-day fall in nearly four years on Friday as growing concerns over China's economy hit world markets.
Many investors said they were nervous about the near-term outlook.
The pan-European FTSEurofirst 300 index closed down 3.40 percent at 1,427.13 points.
The index fell to its lowest level since January and had its worst one-day drop since a 3.44 percent slump in November 2011. It also posted its worst weekly decline since August 2011.
The euro zone's blue-chip Euro STOXX 50 index fell 3.2 percent. Germany's DAX dropped 3 percent, with the DAX nearly 20 percent below record highs reached in April.
Investors across the world were alarmed at the latest Chinese data. The Caixin/Markit manufacturing index showed activity in China's factory sector shrank at its fastest pace in almost 6-1/2 years in August, heightening fears of a slowdown in the world's second-biggest economy.
Vopak was one of the worst-performing stocks in Europe, slumping 15 percent after the Dutch oil and chemicals storage company forecast lower earnings in the second half of the year and warned of tough conditions in Asia.
The Athens stock market also fell 2.5 percent after Greek Prime Minister Alexis Tsipras resigned before a likely new election in September.
"A lot of the good news in Europe had been priced in already, so it doesn't take too much of a global growth scare, along with renewed questions about Greece, to create difficult headwinds for European equities," said Chris Faulkner-MacDonagh, multi-asset strategist at Standard Life Investments.
Tsipras, leader of the leftist Syriza party, is hoping to strengthen his hold on power in the election, after seven months in office in which he fought Greece's creditors for a better bailout deal but had to cave in.
"Regarding Greece, we are not that concerned at the moment, as Syriza is still by far the most popular party. It indicates that Syriza could get enough votes to get an absolute majority," said Antoine Deix, European equity and derivatives strategist at BNP Paribas.
Europe bourses in 2015: link.reuters.com/pap87v
Asset performance in 2015: link.reuters.com/gap87v
Today's European research round-up (Additional reporting by Kit Rees and Sudip Kar-Gupta; Editing by Clelia Oziel)