By Anna Isaac and Frances Yoon

U.S. stocks rose Wednesday on optimism that economic activity is gathering steam and authorities may offer more stimulus to bolster the recovery.

The S&P 500 rose 0.6% after the opening bell, on pace for its third day of gains. The Dow Jones Industrial Average also opened higher, rising about 285 points, or 1.2%.

Investors are cheering signs that the White House and Congress are considering more measures to blunt the impact of historic levels of unemployment on the economy. The Trump administration is examining proposals to provide cash incentives to encourage unemployed Americans to return to work, a top economic adviser said in an interview on Fox News.

"U.S.-China tension has taken a back seat," said Edward Park, deputy chief investment officer at Brooks Macdonald. "A lack of major escalation means markets are more focused on central bank interventions, the levels of liquidity on offer, and economic recovery as countries emerge from lockdowns."

Still, the gains weren't entirely broad, with the tech-heavy Nasdaq Composite down 0.3% in early morning trading. Mega-cap technology companies that powered the stock market's recovery off its March low have lagged in recent days. Facebook lost 1.8% and Netflix shed 0.3%.

Meanwhile, stocks that were pummeled by the coronavirus, including retailers, travel companies and banks, continued their recent rise. American Airlines surged 8.5%, PNC Financial Services Group gained 5.3% and Kohl's rose 11%. Booking Holdings, the parent of Priceline and OpenTable, gained 1.1%.

Outside the U.S., European stocks also ticked higher, with the pan-continental Stoxx Europe 600 advancing 0.5%.

European authorities are also likely to step up stimulus measures, with the European Central Bank likely boosting its bond-buying programs and top officials working toward an agreement on a recovery fund, according to Florian Hense, an economist at Berenberg Bank.

The European Commission is proposing a 750 billion euro ($827 billion) recovery fund in a "turning point" in the response to the crisis, Paolo Gentiloni, the European economy commissioner, tweeted Wednesday.

Among European stocks, car makers were some of the biggest gainers. French President Emmanuel Macron on Tuesday evening said his government planned to spend billions of euros to prop up the country's auto industry amid a collapse in car purchases caused by the coronavirus crisis. Renault rose over 15% in Paris, while Peugeot climbed 5.6%.

"It's the biggest automotive intervention in history," said Demian Flowers, head of automotive research at Commerzbank. But the impact on stocks could be short-lived, based on the experience of 2009, Mr. Flowers said. Incentive programs for consumers can be temporarily effective, bringing forward purchases rather than building sustained demand.

The yield on the benchmark 10-year U.S. Treasury also ticked up Wednesday to 0.699% from 0.697% Tuesday. Yields rise when bond prices fall.

The main gauge for U.S. crude-oil prices edged down 2% to $33.65 a barrel, after rising for seven of the past eight sessions. Russian government officials have signaled that the country may hold off on committing to any extended production cuts ahead of a June meeting among major oil exporters, strategists at ING wrote in a note to clients.

In Asia, the main equity benchmarks reflected mixed sentiment by the close of trading. Japan's Nikkei 225 gained 0.7%. China's Shanghai Composite drifted 0.3% lower.

Financial markets are still fragile, said Daniel Gerard, senior global multiasset strategist at State Street Global Markets. Investors are watching developments on issues such as the pandemic, including prospects for vaccines, and U.S.-China relations, he said.

"It's hard enough in this pandemic to get trade going on because of an uneven recovery," Mr. Gerard said. "If we add complications of the trade war, it will delay a recovery."

The prospect of renewed unrest in Hong Kong is adding to growth concerns for some heavyweight components of the city's Hang Seng, such as financial stocks and developers, according to Mr. Gerard. The index ended the day down 0.4%.

-- Caitlin McCabe contributed to this article.

Write to Anna Isaac at anna.isaac@wsj.com and Frances Yoon at frances.yoon@wsj.com