At least two men are reported to have been injured after being sprayed with suspected toxic water, reports the news agency AFP.
Earlier in the morning, car horns and motorcycle rumbles sounded in the capital - a way for hundreds of protesters to show their displeasure.
People in Myanmar continue to protest, while workers have gone on a nationwide strike in support of ousted leader Aung San Suu Kyi.
- Even though it is a working day today, we will not go to work, even if we receive a salary deduction, 28-year-old Hnin Thazin, who works at a clothing factory, tells AFP.
She was one of more than a thousand people gathered in a park in Yangon on Monday morning - the day a week after the coup, when the military arrested several democratically elected leaders and put them under house arrest, including Aung San Suu Kyi and President Win Myint.
Even in Myanmar's second largest city, Mandalay, trains and chans over a thousand protesters on Monday.
This weekend, tens of thousands demonstrated in the streets around Myanmar in the largest protests so far since the military coup.
The military junta has declared a one-year state of emergency and promises to then hold new democratic elections.
The coup has been met with widespread condemnation from the outside world.