Police in Myanmar have fired rubber bullets and used teargas against protesters defying a ban on large gatherings, in an escalation of the military government’s response to demonstrations against last week’s coup.

Witnesses in Naypyidaw, the remote capital purpose-built by the previous military regime, said police fired rubber bullets at protesters after earlier blasting them with water cannon. A doctor at a clinic in the city told Reuters three people were being treated for suspected rubber bullet wounds.

Earlier, officers had used water cannons to beat back the crowd, and demonstrators had responded by throwing projectiles. Footage on social media showed people running, with the sound of several gunshots in the distance.

Opponents of the 1 February coup gathered in towns and cities across the country for a fourth day of protests on Tuesday, including in Yangon and Mandalay, where evening curfews have been instituted and gatherings of more than five people are banned.

Teargas was used against crowds in Mandalay, where police arrested at least 27 anti-coup demonstrators, including a journalist, media organisations said. A journalist from the Democratic Voice of Burma (DVB) said he was detained after filming the rally. He said people were beaten. Two media organisations also confirmed the arrests.

The military takeover followed an election in November decisively won by Aung San Suu Kyi’s National League for Democracy (NLD) that army leaders claim was fraudulent. The detention of Aung San Suu Kyi sparked outrage across the south-east Asian country of 53 million, and a growing civil disobedience movement affecting hospitals, schools and government offices.

Demonstrations were also held on Tuesday in other cities, including Bago - where city elders negotiated with police to avoid a violent confrontation - and Dawei, and in northern Shan state.

In Magwe in central Myanmar, where water cannons were also used, unconfirmed reports on social media claimed several police officers had crossed over to join the protesters’ ranks. A police officer in Naypyidaw was also said to have switched sides.

As large crowds again gathered near Sule Pagoda in downtown Yangon, one witness estimated there were tens of thousands on the streets by mid morning. Martial law and rumours of incoming soldiers had created an atmosphere of unease, but protesters were determined. Myanmar coup protests grow – in pictures

Pyae Phyo, 33, was gathered with his friends from the Myanmar Seamen Union under the shade of a tree near Sule Pagoda.

“Because of last night’s martial law announcement I thought people may not come,” he said. “But they have come. I am so proud of my people. Every day we will come here. Every day we aren’t free we will protest peacefully for our real leaders, Daw Aung San Suu Kyi and president U Win Myint.”

Earlier Win, 37, a street food vendor, said “Today I heard troops were on their way from Naypyidaw, but that won’t stop the protests.”

The protesters carried anti-coup placards including, “We want our leader”, in reference to Aung San Suu Kyi, and, “No dictatorship”.

Pockets of ambulances manned by a network of volunteer doctors and medical workers were stationed near Sule Pagoda.

Myat Moe Lwin, 25, a graduate doctor, and his colleague Kaung Pyae Sone Thin, 25, were waiting near the ambulances and were prepared to aid protesters injured by water cannon.

“We need to be ready,” he said. “So many people are protesting against the coup. We had to help if there are any problems. It is our professional duty.”

In San Chaung township in Yangon – where large gatherings were banned – scores of teachers marched on the main road, waving a defiant three-finger salute that has become the trademark of resistance to the coup.

“We are not worried about their warning. That’s why we came out today. We cannot accept their excuse of vote fraud. We do not want any military dictatorship,” teacher Thein Win Soe told AFP.

There was confusion over the reach of section 144 of the penal code, which bans gatherings of five or more people. State newspaper The Global New Light of Myanmar announced that two townships in Yangon and others in Mandalay, Sagaing and Kayah state would be subject to the curfew but some believed it was nationwide.

The US embassy said it had received reports of an 8pm to 4am local time curfew in the two biggest cities, Yangon and Mandalay.

Promises on Monday from junta leader Min Aung Hlaing to eventually hold a new election have drawn scorn. In his first address since seizing power, he repeated unproven accusations of fraud in last November’s election. He promised “true and disciplined democracy,” different from previous eras of military rule which left Myanmar in isolation and poverty.

“We will have a multiparty election and we will hand the power to the one who wins in that election, according to the rules of democracy,” he said.

Min Aung Hlaing gave no time frame for the proposed vote, but the junta has said a state of emergency will last one year.

The military also released a statement on state TV on Monday warning that opposition to the junta was unlawful Western governments have widely condemned the coup, although there has been little concrete action. The UN security council has called for the release of Aung San Suu Kyi and other detainees. The UN human rights council will hold a special session on Friday to discuss the crisis, at the behest of Britain and the European Union.