A protester was shot dead in Myanmar's capital Nay Pyi Taw after police opened fire at demonstrators on Tuesday.

The victim was a student, according to reports from Myanmar's media, and six other protesters are receiving medical treatments at hospitals.

This was the first casualty since demonstrations erupted nationwide, following the military's takeover and announcement of a one-year state of emergency at the beginning of February. 

The United Nations (UN) on Tuesday condemned the use of force against protesters in Myanmar. 

"The use of disproportionate force against demonstrators is unacceptable," Ola Almgren, the UN resident coordinator and humanitarian coordinator in Myanmar, said in a statement.

Two protesters were also detained by police in Myanmar's Mandalay on Tuesday, the first arrests made since the protests began.

Martial law was declared in parts of Myanmar's Yangon, Mandalay and Taunggyi on Monday after thousands of people rallied across the country. Limits on gatherings were also imposed in these places, banning people from protesting or gathering in groups of more than five. 

But on Tuesday morning, people were seen gathering in several cities in the country. 

In Yangon, tens of thousands of protesters took to the streets as of 10:00 a.m. and they have forged through several bridges previously blocked by the military early Tuesday morning. 

While in the capital city of Nay Pyi Taw, around 10 people were injured after police used water cannons to disperse protesters. 

(With input from AFP)