WASHINGTON (Reuters) - Republican presidential candidate Donald Trump threatened on Wednesday to slap tariffs on Chinese products to show Beijing that the United States is "not playing games anymore" when it comes to leveling the field on trade.

Addressing a rally in Tampa, Florida, Trump said that if he was elected in November, he would instruct the U.S. trade representative to bring cases against China both in the United States and at the World Trade Organization.

Tariffs would be necessary in some cases "because they have to understand that we're not playing games anymore," he added. Trump had previously pledged a 45 percent tariff on Chinese goods.

Trump said on Wednesday that the trade deficit with China was more than $500 billion, although the figure given by the U.S. government put it at $367 billion in 2015. The United States has brought cases against China at the WTO, and U.S. officials have frequently slapped antidumping and countervailing duties on Chinese products under U.S. law based on complaints brought by U.S. producers.

Trump, who is running behind Democratic presidential candidate Hillary Clinton in opinion polls, has pledged to return manufacturing jobs to America, although many economists believe that the "China shock" has long since passed.

Economists at the Federal Reserve and elsewhere estimate that the "China shock" in the wake of the country's accession to the WTO cost 800,000 to 1 million jobs in the United States. By way of comparison, U.S. manufacturing has shed 5 million jobs since 2000.

(Reporting by Steve Holland; Writing by Tim Ahmann and David Chance; Editing by Frances Kerry and Jonathan Oatis)