A trade war between the world’s two largest economies officially began on Friday morning as the Trump administration followed through with its threat to impose tariffs on $34 billion worth of Chinese products, a significant escalation of a fight that could hurt companies and consumers in both the United States and China. The penalties, which went into effect at 12:01 a.m., prompted quick retaliation by Beijing. China said it immediately put its own similarly sized tariffs on an unspecified clutch of American goods. Previously, the Chinese government had said it would tax pork, soybeans and automobiles, among other goods. In a statement, China’s Ministry of Commerce said the United States “has launched the biggest trade war in economic history so far.” The escalation of the trade war from threat to reality is expected to ripple through global supply chains, raise costs for businesses and consumers and roil global stock markets, which have been volatile in anticipation of a prolonged trade fight between the United States and almost everyone else. “At the moment, I don’t see how this ends,” said Edward Alden, a senior fellow at the Council on Foreign Relations. “This is very much in the president’s hands because he’s got advisers that seem divided, some substantively, some tactically. I just don’t think we’ve had any clear signs of the resolution he wants.” The Trump administration is waging trade wars on multiple fronts as it imposes tariffs on foreign steel, aluminum, solar panels and washing machines from countries like Canada, Mexico, the European Union and Japan. Yet the tariffs on China, the world’s largest manufacturing hub, affect a much larger share of products and a greater percentage of companies that rely on global supply chains, potentially hurting American companies even more than the Chinese firms the Trump administration is targeting. Mr. Trump’s aggressive stance toward China is aimed at pressuring the country to curtail what the White House describes as a pattern of unfair trade practices and theft of American intellectual property. In addition to the tariffs, the White House is placing restrictions on investment and on visas for Chinese nationals. The administration says the trade barriers are being used as leverage to force Beijing to make changes, including opening its markets to American companies and ending its practice of requiring firms operating in China to hand over valuable technology.