Britain's vote to leave the European Union continued to hurt emerging markets on Monday, with currencies and stocks falling from South Africa to Poland as investors fled riskier assets.

The declines highlight how the U.K.'s referendum result, the so-called Brexit, is causing ripple effects across the world, raising uncertainty about global growth and pushing investors into assets they see as safe, such as the U.S. dollar. The dollar's gains are in turn feeding back into the concerns lining up outside emerging markets, making their greenback-denominated debt and the commodities they sell more expensive.

Monday's selloff extended steep falls on Friday, threatening to undo a rally that has boosted emerging markets since the end of January.

The South African rand fell 1.5% to 15.31 rand to the dollar, while the Polish zloty was down 1.2% to 4.058 zloty against the dollar. In China, the yuan fell to its weakest level against the dollar since late 2010, after The People's Bank of China weakened the yuan by the most since August.

The Mexican peso, often seen as a bellwether for the world's emerging markets, was also down on Monday, falling 0.7% against the dollar to 19.05. That follows sharp falls on Friday when, at one point, the peso dropped to its worst level against the dollar on record, 19.52 pesos per dollar, according to FactSet data available back to 1957.

"Brexit has hit sentiment across the board and will have a quite strong impact on emerging markets for the next month or two, at least" said Richard Segal, emerging-market analyst at Manulife Asset Management, which manages $324 billion.

The turbulence comes at a time when emerging market economies were already showing signs of strain. Export growth from emerging economies fell this year to their lowest levels since the financial crisis, according to UBS. After Thursday's referendum, analysts have slashed their forecasts for global growth and that will inevitably reverberate back to the emerging world.

Bank of America Merrill Lynch now predicts that gross domestic product in the European Union will grow by 1.1% next year, down from a forecast of 1.6% before the Brexit vote.

"Europe's recovery is at risk [and the uncertainty] could easily push the eurozone back into stagnation or even recession," said Larry Hatheway, head of multi asset portfolio head at GAM Holding. "In that case, the fallout [for emerging markets] could be considerable."

Mr. Hatheway predicts declines in these markets could be as severe as those seen last August and September and at the start of this year, when concerns over Chinese economic growth rocked emerging markets.

The emerging economies in Central and Eastern Europe are particularly vulnerable, analysts said. The U.K. is Poland's third-biggest export destination and more than half a million Poles live in Britain, many of whom send remittances back home. The Polish stock market was down 1.4% on Monday. In the Czech Republic, the PX-50 shed 3.9% by midday. Hungary's currency, the forint, is down 1.4% against the dollar.

The effects were palpable even in China, the world's second-largest market. The central bank fixed the yuan at 6.6375 to the dollar from Friday's midpoint of 6.5776, the weakest level for the domestic currency since Dec. 24, 2010.

"The market should be a little bit disappointed as most of the traders hoped that China's central bank should offer some sort of 'stability' amid rising market uncertainties," Zhou Hao, senior economist for emerging markets in Asia at Commerzbank AG. "Undoubtedly, today's [yuan] fixing rates hint that the market should be prepared for more volatility."

Gains in the dollar are key for emerging markets. As domestic currencies fall, dollar-denominated debt becomes more expensive to service and pay back.

As of the third quarter of 2015, the Bank for International Settlements estimates there was about $1.1 trillion in dollar-denominated bonds issued by nonbank emerging-market companies outstanding, up from $509 billion at the end of 2008.

The rising dollar is making commodities more expensive for holders of other currencies, threatening to dent demand in everything from oil to copper.

Emerging markets, particularly in Africa and South America, are big commodities exporters.

Brent crude, the international oil benchmark, fell 1.6% on Monday after shedding 4.9% on Friday while all base metals were lower.

Top commodities player South Africa is being hit in other ways. The country's wide current-account deficit and tight trade ties to Europe and the U.K. have made its rand currency particularly vulnerable to the Brexit-linked turmoil. The rand slumped against the U.S. dollar on Friday after the results of U.K.'s referendum were announced.

Hours after the result was announced on Friday, President Jacob Zuma said that "the uncertainty that arises from this vote means the volatility that has characterized capital markets in the lead-up to the vote may persist."

Still, central bank policy in the wake of the Brexit vote might help cushion the blow for emerging markets. Lower-for-longer interest rates in the developing world would make those markets more attractive for yield-seeking investors.

Federal-funds futures, used by investors and traders to place bets on the Federal Reserve's policy, now show any U.S. interest-rate increase this year as very unlikely, CME Group data show. Investors also now expect the Bank of England to cut interest rates there.

"Brexit is generally negative for growth but could end up helping emerging countries, especially in Asia, as it pushes back the Fed raise," said Brett Diment, head of emerging market debt at Aberdeen Asset Management.

Patrick McGroarty in Johannesburg and Ewen Chew in Singapore contributed to this article.

Write to Georgi Kantchev at georgi.kantchev@wsj.com

(END) Dow Jones Newswires

June 27, 2016 09:45 ET (13:45 GMT)