The protests have gathered momentum since Wednesday when some people broke through police barriers protecting the mine, operated by Myanmar Wanbao, a unit of a Chinese weapons maker, residents of the area told Reuters by telephone.
Myanmar Wanbao runs the Letpadaung mine in a joint venture with a conglomerate controlled by the Myanmar military, Myanmar Economic Holdings Ltd.
Villagers say their land has been unlawfully confiscated to expand the mine.
After big protests in 2012 and 2013, when riot police raided a protest camp injuring more than 100 people, then opposition leader Aung San Suu Kyi led an inquiry that recommended compensating the residents and minimizing environmental damage.
Suu Kyi led her party to a sweeping election victory last year and now oversees the government.
"The Chinese haven't done anything to fulfil their obligations mentioned in Daw Aung San Suu Kyi's report," Ma Mar Cho, one of the protest leaders, told Reuters by phone.
Myanmar Wanbao representatives did not answer requests for comment on Friday.
A spokesman at Suu Kyi's office said the government was monitoring the situation and the company's response to earlier inquiry recommendations.
"We are checking how the company has fulfilled the commission's requirements with the respective ministries," said Zaw Htay, spokesman at the State Counselor' Office, run by Suu Kyi.
Work at the mine, about 100 km (60 miles) west of the city of Mandalay, was suspended after the 2012-13 protests. The company has recently tried to show it can reduce the impact of mining and improve livelihoods.
The protests could strain a delicate relationship between Suu Kyi's party and the military, which maintains a major political role with control of three important ministries, that includes oversight of police, and holds a quarter of seats in parliament.
China will also likely be watching how the new government handles the protests. It has made a big push to assert its business and political interests since Suu Kyi's party took over in April.
In 2012, police threw phosphorus at protesters, inflicting serious burns on scores. In 2014, a protester was shot dead.
"There hasn't been any response from anybody to the protesters' letters," said Ar Lawka, a Buddhist monk who supports the protests, referring to villagers' letters to the mine operator and lawmakers form Suu Kyi's party.
"This is not the last protest."