The launch came hours after U.S. President Donald Trump described North Korea's pursuit of a nuclear arsenal as a "humanity problem" and a senior U.S. official told reporters that the "clock has now run out" on Pyongyang.
Seoul's Joint Chiefs of Staff said in a statement that the missile fired from the North's eastern coastal town of Sinpo on Wednesday morning flew about 37 miles. It gave no further details.
Wednesday's firing was made as South Korean and U.S. troops were conducting annual military drills that the North views as an invasion rehearsal. North Korea often responds to the drills with its own military training and harsh rhetoric.
Two weeks ago, the South Korean and U.S. militaries said they detected what they called a failed North Korean ballistic missile launch.
A White House official also said Tuesday that "all options are on the table" for the U.S., though the official would not say what steps Trump was willing to take to curb dictator Kim Jong Un's pursuit of a nuclear weapon.
Trump and Chinese President Xi Jinping will huddle Thursday and Friday at Trump's Mar-a-Lago estate in Florida, a venue chosen to give the summit a more informal feel. White House officials said Tuesday that trade and security would be high on the new American president's agenda, including pushing China to exert more economic pressure on North Korea.
China continues to oppose the tough measures demanded of it to address the issue, fearing a collapse of the Pyongyang regime would bring a crush of refugees and possibly U.S. and South Korean troops on its border.
Trump told the Financial Times over the weekend that the U.S. is prepared to act alone if China does not take a tougher stand against North Korea's nuclear program.
"China has great influence over North Korea," Trump said. "And China will either decide to help us with North Korea, or they won't. And if they do that will be very good for China, and if they don't it won't be good for anyone."
The Associated Press contributed to this report.