The army said it had carried out the detentions in response to "election fraud," handing power to military chief Min Aung Hlaing and imposing a state of emergency for one year, according to a statement on a military-owned television station.
The generals made their move hours before parliament had been due to sit for the first time since the NLD's landslide win in a Nov. 8 election viewed as a referendum on Suu Kyi's fledgling democratic government.
Phone lines to the capital Naypyitaw and the main commercial center of Yangon were not reachable, and state TV went off air. People rushed to markets in Yangon to stock up on food and supplies while others lined up at ATMs to withdraw cash.
Soldiers took up positions at city hall in Yangon and mobile internet data and phone services in the NLD stronghold were disrupted, residents said. Internet connectivity also had fallen dramatically, monitoring service NetBlocks said.
Suu Kyi, Myanmar President Win Myint and other NLD leaders had been "taken" in the early hours of the morning, NLD spokesman Myo Nyunt told Reuters by phone.
"I want to tell our people not to respond rashly and I want them to act according to the law," he said, adding that he expected to be arrested himself. Reuters was subsequently unable to contact him.
A video posted to Facebook by one MP appeared to show the arrest of another, regional lawmaker Pa Pa Han.
In the video, her husband pleads with men in military garb standing outside the gate. A young child can be seen clinging to his chest and wailing.
The detentions came after days of escalating tension between the civilian government and the military that stirred fears of a coup in the aftermath of the election.
Suu Kyi's party won 83% of the vote in only the second election since a military junta agreed to share power in 2011.
The White House said President Joe Biden had been briefed on the arrests and Secretary of State Antony Blinken called for the leaders' release.
"The United States stands with the people of Burma in their aspirations for democracy, freedom, peace, and development. The military must reverse these actions immediately," he said in a statement, using an alternative name for Myanmar.
U.N. Secretary-General Antonio Guterres condemned the detention of Suu Kyi and other political leaders and "urges the military leadership to respect the will of the people of Myanmar," a U.N. spokesman said.
The Australian government said it was "deeply concerned at reports the Myanmar military is once again seeking to seize control of Myanmar."
Japan said it was watching the situation and had no plans to repatriate Japanese nationals from Myanmar, while India's foreign ministry expressed deep concerns about the coup.
Singapore had "grave" concern about the unfolding situation in Myanmar and urged all sides to work towards a peaceful outcome, its foreign ministry said.
LEAD-UP TO COUP
Nobel Peace Prize winner Suu Kyi, 75, came to power after a 2015 election win that followed decades of house arrest in a struggle for democracy with Myanmar's junta that turned her into an international icon.
Her international standing was damaged after hundreds of thousands of Rohingya fled army operations into refuge from Myanmar's western Rakhine state in 2017, but she remains hugely popular at home.
Political tensions soared last week when a military spokesman declined to rule out a coup ahead of the new parliament convening on Monday, and military chief Min Aung Hlaing raised the prospect of repealing the constitution.
Tanks were deployed in some streets last week and pro-military demonstrations have taken place in some cities ahead of the first gathering of parliament.
Myanmar's election commission has rejected the military's allegations of vote fraud.
The country's constitution, published in 2008 after decades of military rule, reserves 25% of seats in parliament for the military and control of three key ministries in Suu Kyi's administration.
In its statement declaring the state of emergency, the military cited the failure of the electoral commission to address complaints over voter lists, its refusal to agree to a request to postpone new parliamentary sessions and protests by groups unhappy over the election.
"Unless this problem is resolved, it will obstruct the path to democracy and it must therefore be resolved according to the law," the statement said, citing an emergency provision in the constitution in the event national sovereignty is threatened.
Daniel Russel, the top U.S. diplomat for East Asia under former President Barack Obama, who fostered close ties with Suu Kyi, described the military takeover as a severe blow to democracy in the region.
"If true, this is a huge setback - not only for democracy in Myanmar, but for U.S. interests. It’s yet another reminder that the extended absence of credible and steady U.S. engagement in the region has emboldened anti-democratic forces," he said.
Human Rights Watch's Asia advocacy director, John Sifton, criticized the initial White House response as “disappointingly weak” and urged a more concerted international reaction.
“The U.S. needs to work with allies to speak more clearly, in unison, in terms of ultimatums, to put the Myanmar military on notice of the specific consequences that will occur if their coup is not reversed," he said.