The test was of a medium- or intermediate-range missile that landed in the Sea of Japan, according to the US defense department, not an Intercontinental Ballistic Missile (ICBM), which the North has said it could test at any time, Reuters reported.
The launch marks the first test of Trump's vow to get tough on an isolated North Korean regime that last year tested nuclear devices and ballistic missiles at an unprecedented rate in violation of United Nations resolutions.
A US official said the Trump administration had been expecting a North Korean "provocation" soon after taking office and will consider a full range of options in response, but these would be calibrated to show US resolve while avoiding escalation.
The new administration is also likely to step up pressure on China to rein in North Korea, reflecting Trump's previously stated view that Beijing has not done enough on this front, the official said, speaking on condition of anonymity.
"This was no surprise," the official said. "The North Korean leader likes to draw attention at times like this."
The latest test comes a day after Trump held a summit meeting with Japanese Prime Minister Shinzo Abe, and also follows Trump's phone call last week with Chinese President Xi Jinping.
Trump has pledged a more assertive approach to North Korea but given no clear sign of how his policy would differ from Obama's so-called strategic patience. In January, Trump tweeted "It won’t happen!" after Kim said the North was close to testing an ICBM, but his aides never explained how he would do so.
The missile was launched from an area called Panghyon in North Korea's western region just before 8 a.m. (2300 GMT Saturday) and flew about 500 km (300 miles), the South's Office of the Joint Chiefs of Staff said.