For American investors, Britain’s vote to break up with Europe didn’t just deliver stocks a bad day. It stirred worries about a global economic slowdown — and weighty questions about a wave of voter discontent that is dominating US politics as well.

Britain “is one theater in a very large campaign,’’ said Jurrien Timmer, director of global macro strategy at Fidelity Investments in Boston. “The US election is another theater, with the common denominator of slow growth and disenfranchisement.’’

The major US stock indexes declined more than 3 percent Friday, and the Dow Jones Industrial Average plunged more than 600 points, wiping out all its gains for 2016. Meanwhile, investors rushed into the relative safe havens of US Treasuries, and gold climbed nearly 5 percent.

Big moves will probably continue in the coming days, as markets try to sort out how Britain’s withdrawal from the European Union will affect the rest of the world. In the near term, US interest rates are likely to stay low, analysts said, but weakness in Europe, plus a stronger dollar, would eventually affect stocks this side of the Atlantic.

“We think we’re shaping up for some pretty significant volatility for the balance of the year,’’ said Lori Heinel, chief portfolio strategist at State Street Global Advisors, a large Boston-based investment manager.

Already State Street had been downgrading its view of the economy, Heinel said. “This only heightens the risk of a downside.’’

The $60 billion Massachusetts state pension fund warned that the British vote, dubbed Brexit, could deliver the Pension Reserves Investment Trust a loss of at least 1.5 percent and as much as 9 percent in a worst-case scenario.

Britain’s separation from Europe could take at least two years to play out, so there’s no immediate change taking place. But the move creates uncertainty. And the UK is a major global financial center, in addition to being the fifth-largest economy in the world.

“I’m worried about a slowdown. I’m worried about the nascent recovery we saw on the continent getting derailed,’’ said Jeff Knight, global head of asset ­allocation at Columbia Threadneedle, a Boston-based investment manager that oversees $464 billion. “This is the beginning of the issues, not the end.’’

For retirement investors whose portfolios took a hit during the 2008 recession, this could represent another major jolt in a period when stock returns have been positive but hardly overwhelming. For example, through Thursday, the Standard & Poor’s 500 Index was up 4.5 percent for the year; the Dow had been up 3.4 percent.

Vanguard Group of Valley Forge, Pa., which manages $3.5 trillion, including the retirement funds of many Americans, said the UK vote “will have a significant global economic impact.’’

The change “will affect global markets, with a likely decrease in the value of riskier assets such as stocks,’’ Vanguard said, though it and other firms advised investors to stick to a diversified approach. Trying to time the market or sell off UK assets could backfire, the firm said.

Some investment specialists remain bullish on the US economy for now.

“I don’t see an impact to the US economy — except maybe a pull back on capital spending,’’ said renowned bond manager Dan Fuss, vice chairman of Loomis, Sayles & Co. in Boston, in an e-mail. He also said there was now virtually zero chance of the Federal Reserve raising interest rates further this year.

But more broadly, he called the vote “discouraging geopolitical news.’’

Indeed, Robert Mahoney, chief executive of Belmont Savings Bank, said British bankers who attended a meeting in Boston on Friday were gloomy over the Brexit news. The financial establishment wanted to remain part of the European Union, while voters angry over stagnant wages and immigration prevailed.

“The parallel for the US is just breathtaking,’’ Mahoney said.

President Obama on Friday said both the UK and the European Union were important partners of the United States. He said the vote pointed to the ongoing challenges of globalization.

Fidelity’s Timmer said, “The UK vote does suggest that this very long era of globalization — healthy growth with very low inflation — it might not be reversing, but it’s sort of peaking.’’ If that’s the case, he explained, “We may have slower growth and more inflation going forward.’’

US financial regulators said they were monitoring the markets to make sure they functioned properly given the volatility, and to minimize their effect on the economy. The Fed said it stood ready to work with other central banks to provide liquidity to the markets if necessary.

The Bank of England said it could infuse the equivalent of $342 billion into the financial system if needed.

John Canally, chief economic strategist for LPL Financial Holdings Inc., a national brokerage firm based in Boston, said, “I don’t think this is enough to push us into a recession.’’ This event is different from, say, the financial crisis, when the country had been on a borrowing binge, and the tech bubble before that, when stocks were overvalued, he said.

But policymakers’ reaction to Brexit will be important, he said. And the question is how negative the drumbeat of news is in the coming weeks and months, given the economy’s relatively slow growth.

“When the top is spinning slowly and it gets nudged a bit,’’ Canally said, “there’s a chance that it falls over.’’

Beth Healy can be reached at beth.healy@globe.com. Follow her on Twitter @HealyBeth.