The test verified the combat effectiveness of the overall system, and North Korean leader Kim Jong-un predicted "it would be an inescapable distress to the forces becoming a fat target of the weapon", state news agency KCNA said.
North Korean leader Kim Jong-un on Wednesday oversaw the first test firing of a "new-type large-caliber multiple launch guided rocket system", North Korean state media reported on Thursday.
The rocket system "will play a main role in ground military operations", KCNA reported.
The report comes a day after the South Korean military said North Korea fired at least two missiles from its east coast into the sea.
Wednesday's launches were from the Wonsan area on North Korea's eastern coast, from which last week's missiles had been fired, South Korea's Joint Chiefs of Staff (JCS) said in a statement.
The JCS said later the North had fired ballistic missiles that flew about 250 km (155 miles).
UN Security Council to meet on North Korea missile launches
Britain, Germany and France have asked the United Nations Security Council to meet behind closed doors on Thursday on North Korea's latest missile launches, diplomats said.
South Korea's Joint Chiefs of Staff say in a statement that the two devices were fired from the Wonsan area on the east coast at dawn and flew around 250 km, a move that has triggered UN Security Council members to call for an emergency meeting.
South Korea said Pyongyang fired two ballistic missiles on Wednesday, days after a similar launch that the nuclear-armed North described as a warning to the South over planned joint military drills with the United States.
The two devices were fired from the Wonsan area on the east coast at dawn and flew around 250 kilometres, said South Korea's Joint Chiefs of Staff.
"We stress a series of missile launches do not help ease tensions in the Korean Peninsula and urge the North to refrain from such acts," they said in a statement.
The North is banned from ballistic missile launches under UN Security Council resolutions but it was the second such firing in less than a week, despite a meeting between leader Kim Jong-un and US President Donald Trump last month.
Pyongyang and Washington are engaged in a long-running diplomatic process over the North's nuclear and missile programmes that has seen three high-profile encounters between their leaders in the space of a year.
They agreed to resume talks during their impromptu June encounter in the Demilitarised Zone, which divides the peninsula, but that working-level dialogue has yet to begin.
Pyongyang has warned the negotiations could be derailed by Washington and Seoul's refusal to scrap the annual manoeuvres between their forces.
The North has defied years of isolation and sanctions to develop its arsenal and has not given up any of its weapons, while proving itself adept at dragging out discussions.
US Secretary of State Mike Pompeo told reporters that the talks were taking "a little bit longer" than expected to start.
There was no immediate comment from Pyongyang on the latest launch, but Harry Kazianis of the Center for the National Interest in Washington said it was a warning to the two security allies to stop the exercises "or we will continue to show off our own offensive military capabilities and raise tensions to a slow boil over time."
The North will carry out more launches before the drills begin next week and again afterwards, he predicted.
"The only question is: would the Kim regime dare test an ICBM, or a long-range missile, that could hit the US homeland?"
Pyongyang said last Thursday's launches were of newly designed "tactical guided weapons" that were a "solemn warning to the South Korean warmongers" over the planned military drills with the US.
Washington stations nearly 30,000 troops in the South to defend it from its neighbour, which invaded in 1950.
The devices were widely described as ballistic missiles, including by the US-South Korean Combined Forces Command and the government in Seoul.
But Trump — who has repeatedly touted his relationship with Kim, whose regime is widely accused of human rights abuses — brushed off the North's bellicose language, saying it was warning Seoul rather than Washington.
"He didn't send a warning to the United States," Trump said.
"They have their disputes, the two of them have their disputes."
Trump says he's not worried about North Korea testing missiles because they're just "short-range" and "my relationship is very good with Chairman Kim." He downplays the situation by saying that North and South Korea "have their disputes ... they've had 'em for a long time." pic.twitter.com/aVOzwGxM7B— Aaron Rupar (@atrupar) July 26, 2019
The Korea Times condemned what it called the US president's "willful ignorance" in an editorial on Tuesday, before the latest launches.
Trump "gives the impression that he doesn't mind its missile launches as long as they are short-range, and not threatening the US," it said.
"Such a way of thinking is frustrating — and dangerous," it added. "Most of all, he can give the wrong signal to the North that the US will not step in as long as it does not target the US mainland. What about US allies in Asia?"