President Trump imposed steep tariffs on steel and aluminum imports on Thursday, singling out China as a top offender in an effort to curb what he has called unfair trade practices. But there is little evidence to support his dismissal of estimates that say Chinese steel accounts for only a small percentage of imports into the United States.

We fact-checked Mr. Trump’s targeting of China’s trade practices this week.

“Transshipping, frankly, is a big deal. China says it’s got 2 percent, but it sends much more.” — March 8.This lacks evidence.

Mr. Trump repeated this claim as he prepared to announce the tariffs. “I’ve watched where the reporters have been writing, 2 percent of our steel comes from China. Well, that’s not right,” Mr. Trump said at a news conference on Tuesday. “They transship all through other countries.”

“They send us a much, much higher level than that, but it’s called transshipping,” he added.

Transshipping refers to a practice in which one country exports a product to another country after it passes it through a third country. It is illegal when done to falsify or disguise the product’s country of origin and to evade duties and tariffs.

There is little evidence to support Mr. Trump’s claim that the volume of Chinese steel imports is “much higher” after transshipping.

First, the 2 percent estimate does not come from China, as Mr. Trump said, but from his own Commerce Department. Its data suggests that Chinese steel accounts for just 2 percent of total imports to the United States by quantity last year, and about 3.5 percent by value.

Asked to explain Mr. Trump’s claim, a White House official who spoke on condition of anonymity acknowledged that countervailing and anti-dumping duties have significantly reduced Chinese steel imports. The United States has imposed 24 trade remedies against steel from China, more than any other country, covering an estimated 90 percent of Chinese imports.

Asked for more details, the White House said in a statement that China had found ways to circumvent those barriers, simply by passing steel products through a third country. But, the statement said, “more often they are lightly processed into a new product (harder to quantify and catch) before being shipped Stateside.”