The global stock market slump has entered its second week, pushing the UK's main share index below 6,000 for the first time since October.
Stock markets look set for a wobbly ride this week, analysts said
The key US Dow Jones index remained positive for most of Monday, but fell
towards the end of the session to close down 63.7 points, or 0.5%, at 12,050.4.
By the end of trade in London the FTSE 100 had recovered, but it still closed down 57.5 points, or 0.9%, at 6,058.7.
In the past five sessions, about £111bn has been wiped off the FTSE's value.
Elsewhere on Wall Street, the technology-laden Nasdaq index closed down 1.1% at 2,340.7, while the S&P 500 index closed down 0.9% at 1,374.12.
The drop mirrored heavy losses in Europe and Asia, with investors dumping stocks because of concerns they are overvalued and growth will slow.
With investors getting increasingly jittery, the steep falls on the stock exchanges have started to ripple through to the commodities markets, and especially oil.
A barrel of US sweet crude was down by $1.38 a barrel to $60.26, while Brent crude dropped $1.37 to $60.71 on the ICE Futures exchange in London.
The current stock slump was triggered last week by the biggest drop on China's market in a decade.
That fed into fears about the state of the US economy at a time when many investors were questioning whether share prices had risen too far too quickly.
Many of the world's top indexes and shares had climbed to levels not seen since the dotcom bubble burst in 2000.
On Monday, Japan's Nikkei 225 had its worst day since June - largely a result of the continued rise in the yen - which hit its highest rate against the dollar in three months.
A strong currency makes Japanese goods more expensive abroad and cuts the profits of Japanese firms when overseas earnings are brought home.
It also means that investors who borrowed yen to take advantage of low interest rates and then put the cash into assets such as equities, would now be looking to close positions and pay off their loans, analysts said.
Leading declines on Monday in Tokyo were exporters such as Toyota Motor and Canon, and the Nikkei closed 3.4%, or 575.68 points, lower at 16,642.25, its lowest level since December and the largest daily plunge since June 2006.
Shanghai's composite index lost 3.5%, Taiwan shares closed down 3.7%, and the main Indian market had its lowest close in five months.
In Europe, France's Cac and Germany's Dax indexes also slipped, both losing more than 0.7% and 1% respectively.
Volatility probably will continue as riskier assets are sold, analysts said.
"When there's such a big market move in such a short period of time, there's that element of surprise and confusion," said Teruhisa Ishikawa of Mizuho Investors Securities.
Is this the start of a worldwide depression? Or is it a mere blip in the market? Are you worried about your investments? How do you think this will affect the economy in your country?
The BBC may edit your comments and not all emails will be published. Your comments may be published on any BBC media worldwide.