Concerns about the Chinese economy hit global stocks Wednesday and could make for a weak start on U.S. markets.
U.S. stock futures were modestly lower ahead of a quiet day in terms of U.S. economic and corporate news.
Big swings in some commodities reflected the nervousness about the pace of growth in the world's second biggest economy. Gold prices pushed higher while copper prices fell to their lowest level in at least a year.
"It was the accumulation of negative China-related headlines or it was the sharp drop in copper in both London and Shanghai that spooked markets," wrote Deutsche Bank analyst Jim Reid in a market report.
China concerns have been edging to the forefront of investors' minds since February data showed exports tumbled 18% compared to last year.
That followed news that the country had experienced its first-ever corporate debt default. Some analysts believe more defaults could be in the pipeline.
In recent weeks, the Chinese central bank has also loosened its grip on the currency, allowing it to fluctuate more than usual, shaking confidence in what has been seen as a safe one-way bet.
Plug Power ( and rival fuel cell stocks )Ballard Power System ( and )FuelCell Energy ( were all down dramatically in premarket trading. The companies are considered highly speculative and have enjoyed a )massive run as of late.
U.S. stocks closed slightly lower Tuesday.