In footage shared with Reuters, protesters were seen carrying out an injured man in Hlaing township in the Yangon region, ducking and taking cover amid sounds of gunfire, also on Saturday, which was the bloodiest day since the coup on February 1.
Across Myanmar, opponents of the ruling junta on Sunday mourned the killings of at least 114 people by security forces, but vowed to keep protesting to end army rule.
Children were among those killed on Saturday, Myanmar's Armed Forces Day, according to news reports and witnesses, in a crackdown that drew renewed Western criticism.
The UN investigator said the army was carrying out "mass murder." Saturday also brought some of the heaviest fighting since the coup between the army and the ethnic armed groups that control swathes of the country.