Live-stream images shared on social media platforms before the internet blackout showed more military vehicles and soldiers moving through others parts of the country.
The Feb. 1 coup and the arrest of Nobel peace prize victor Suu Kyi and others have sparked the biggest protests in Myanmar in more than a decade, with hundreds of thousands coming onto the streets to denounce the military's derailment of the country's tentative transition to democracy.
Myanmar's military leaders have extended their detention of Suu Kyi, whose remand was set to expire on Monday, until February 17, according to her lawyer Khin Maung Zaw, reported AP.
More than a dozen police trucks with four water cannon vehicles were deployed on Monday near the Sule Pagoda in central Yangon, which has been one of the main demonstration sites in the commercial capital, as groups of protesters gathered outside the central bank and the Chinese embassy.
Hundreds of engineering and technology students protested in a northern district of the city, according to an AFP journalist.
Some carried banners against the military that read: "They kill in (the) day. They lie on TV".
Monitoring group NetBlocks reported that a "state-ordered information blackout" had taken Myanmar nearly entirely offline, but services began resuming around the start of the working day. It circulated widely on social media, as did a notice said to be from service provider Oredoo Myanmar containing the same details.
Footage broadcast live on Facebook showed the crowd being shot at by security personnel, but it is not clear whether they were using rubber or real bullets.
Media outlet The 74 Media, based in the northern city of Myitkyina, said that five journalists had been arrested after clashes between police and protesters.
Western countries - from the European Union, Britain, Canada and 11 other nations - issued a statement late on Sunday calling on security forces to "refrain from violence against demonstrators and civilians, who are protesting the overthrow of their legitimate government".
"The government the people of Myanmar chose has been taken from us", one organizer said through a megaphone as protesters were gathering at Yoyogi Park before marching toward the scramble crossing near Shibuya Station.
UN Secretary-General Antonio Guterres called on the military authorities to allow the UN special envoy for Myanmar to visit the country. The leadership of Myanmar's electoral commission has also reportedly been detained.
The U.S. Embassy in Yangon warned there was a possibility of an internet interruption overnight between 1:00 a.m. and 9:00 a.m. local time. Senior General Min Aung Hlaing, who led the coup, promised last week in a nationally televised speech that new elections would be held to bring a "true and disciplined democracy", but did not specify when they would take place.
Suu Kyi, who has been known for decades to be the torchbearer in the fight for democracy in the country, even faces charges of illegally importing and using six walkie-talkie radios that were found during a raid of her house.
The Assistance Association for Former Political Prisoners, a Myanmar monitoring group, said at least 384 people have been detained across the country since the coup, mostly in night raids.
Tributes to the woman were held Sunday by protesters in Yangon and Mandalay, Myanmar's second-biggest city.
In the southern city of Dawei, seven police officers broke ranks to join anti-coup protesters, mirroring local media reports of isolated defections from the force in recent days.
As well as the mass protests across Myanmar, the country's military rulers were faced with a strike by government workers, part of a civil disobedience movement to protest the coup.
"We don't trust anyone at this time, especially those with uniforms", said Myo Ko Ko, member of a street patrol in Yangon. They condemned the arrests of political leaders and activists as well as the military's interference with communications.
The junta insists it took power lawfully.