U.S. stock-index futures slumped on Wednesday, as shares in Europe and Asia fell on ongoing concerns about China's economy and the turmoil in Ukraine.
The dollar, gold and Treasury prices rose, pushing the yield on the 10-year note down 2 basis points to 2.746 percent. Crude-oil futures fell.
(Track: European shares live)
Tai Hui, chief market strategist for Asia at J.P. Morgan Funds, told CNBC: "The timing of this volatility coincided with a level of pessimism on China that we haven't seen for quite some time."
The possibility of sanctions against Russia loomed on Wednesday, after reports that the G-7 group of countries will declare Russia's annexation of Ukraine's Crimea region a violation of international law.
"Concerns about the Ukrainian situation are unlikely to go away given that EU leaders seem determined to implement some form of sanctions against allies of President Putin, which could, in turn prompt a counter response," Michael Hewson, a chief market analyst at CMC Markets said in a morning note on Wednesday.
In the U.S., the day will be a quiet one for scheduled economic and corporate news, with the weekly MBA Mortgage Index the main feature on the data docket. There will also be weekly crude inventories at 10:30 a.m. ET and the Treasury's budget for February at 2 p.m.
No major U.S. companies are expected to report quarterly results before Wall Street opens on Wednesday.
Copper was in the spotlight on Wednesday after prices fell to their lowest level in nearly four years overnight. Selling was intensified by worries about cooling Chinese demand and the liquidation of inventories used for finance deals.
(Read more: Are Dr Copper's daysnumbered?)
—By CNBC's Katy Barnato