By Rob Wile
U.S. stocks opened higher Tuesday, bringing momentary relief from a massive multi-day sell-off in response to President Donald Trump's tariffs shock and even as trade tensions between the U.S. and China heated up.

The S&P 500 climbed more than 3.8%. The tech-heavy Nasdaq was about 4% higher. The Dow Jones Industrial Average gained more than 3.6% or nearly 1,400 points.

The reasons for the bounce are idiosyncratic. Some markets in Asia traded higher overnight — though this was partially in response to Chinese state funds stepping in to serve as a backstop to recent drawdowns. Japan's Nikkei stock index also surged 6% after the White House indicated it was opening bilateral trade negotiations with the longtime U.S. ally.

European stocks climbed too, led by stronger outlooks in defense groups.

U.S. indexes were also getting a boost from a better outlook for health insurance stocks, which come as the Centers for Medicare & Medicaid Services on Monday announced a 5.06% increase in Medicare payments for next year — significantly higher than expected.

But some analysts suggested the bounce may simply be attributable to lower volumes of shares being traded, which tends to make overall market moves bigger than any actual change in earnings outlooks.

"Markets remain relatively thin and skittish," ” said William Press Steve Sosnick, chief strategist at Interactive Brokers financial group. "So each of these moves get amplified, that’s what we're seeing today: a little bit of bargain hunting, which does make sense, but then we're also seeing a little bit of a feeding frenzy that gets amplified."

A brief rally Monday sparked by a false report on social media has also revealed that many traders were positioned to buy stocks on any news of a reversal in Trump's policies, and some of that impact may be lingering, Sosnick said.

Around 9:10 a.m., Trump posted to social media that China "wants to make a deal, badly" and that he had held positive discussions with the acting president of South Korea about negotiating one with that nation as well.

Still, there was little indication that Trump was set to meaningfully relent on his effort to impose massive tariffs on U.S. imports, which the president has said are designed to bring manufacturing jobs back and close U.S trade deficits.