Amid multiple but unconfirmed reports of massacres and evidence of the widespread torching of villages, Foreign Minister Julie Bishop said "we have emphasised Myanmar's responsibility to provide protection and humanitarian assistance to people in Rakhine, regardless of ethnicity or citizenship status".

Nearly 400 people have died in the fighting that has rocked the state for a week, according to new official data cited by Reuters.

Ms Bishop said Australia, one of the largest aid donors to Rakhine, has expressed "deep concerns", including to Myanmar's de facto leader Aung San Suu Kyi.

Twenty-six Rohingya, most of them women and children, drowned while attempting to escape the escalating violence on Thursday. Their bodies washed up in Bagladesh after their boat capsized on the Naf River that divides the two countries. Bangladesh border guards said Myanmar police fired on at least one of the boats making the crossing.

Almost 40,000 Rohingya Muslims have fled the violence since last Friday and tens of thousands more are expected to attempt to make the perilous journey in the coming days.

About 20,000 of them are stranded in no man's land between the two countries.

Bangladesh has refused to open its border posts despite appeals from the International Organisation for Migration and UN Secretary-General Antonio Guterres.

Myanmar's army says it is carrying out clearance operations to defend the country against "terrorists" who attacked 30 police posts last Friday.

But fleeing Rohingya say the army and Buddhist vigilantes have unleashed a campaign of killings and burnings.

An insurgent group, the Arakan Rohingya Salvation Army, claimed responsible for Friday's attacks.

The US has made a stronger intervention than Australia, calling on Myanmar's security forces to stop attacking civilians and aid workers.

"As Burmese security forces act to prevent further violence they have a responsibility to adhere to international humanitarian law, which includes refraining from attacking innocent civilians and humanitarian workers and ensuring assistance reaches those in need," said Nikki Haley, US ambassador to the UN.

The United Nations Security Council also urged a de-escalation of the violence.

Matthew Rycroft, Britain's ambassador to the UN, said UN council members discussed recommendations aimed at ending the crisis during a closed meeting but no formal statement was issued.

"We condemned all the violence. We called on all parties to de-escalate," he said.

More than 250 NGOs and civil society groups in Myanmar have issued a statement urging the government to protect the rights of all its citizens.

But fire-brand nationalistic monk U Wirathu accused "marauding" Muslims of attacking villages, labelled aid groups working in Rakhine "terrorists" and called for the imposition of martial law.

Authorities in Bangladesh have warned that Rohingya are becoming increasingly desperate and are taking to unsafe boats to flee.

Reporters on the Bangladesh side of the border have heard gunfire and explosions and seen smoke rising from villages.

Chris Lewa from the Rohingya monitoring group The Arakan Project, said it appeared Myanmar security forces are trying to drive out a large proportion of the Rohingya population.

She also said that ethnic Rakhine vigilantes are "actively participating in the burning of villages".

"We're hearing burning, burning, burning and it seems to be spreading from south to the north."

Tun Kin, president of Burmese Rohingya Organisation UK said his organisation has confirmed more than 1000 deaths in Rakhine "but the figure is probably much higher".

"The military is systematically going from village to village, looting and destroying everything," he said.

"They leave nothing behind. There is nothing for Rohingya to return to."

Mohammed Rashid, 45, one of the arrivals in Bangladesh, said bullet splinters hit under his eye after the Myanmar army fired on a group of Rohingya.

"We hid in the forest for two days and then we were stopped at the border - but we got through," he said.

"We heard the houses in our village have been burned down."

More than 1.1 million Rohingya in Rakhine are denied citizenship, freedom of movement and other rights despite having lived in Buddhist-majority Myanmar for generations.

There have been waves of deadly violence in the state for years.

The latest bloodshed comes just days after an international commission led by former UN Secretary-General Kofi Annan warned of more radicalisation if ethnic tensions in Rakhine were not addressed.

Late last year United Nations investigators detailed mass rapes, killings, brutal beatings, the torching of homes and forced disappearances by Myanmar security forces.

The UN said the "devastating cruelty" could amount to crimes against humanity and "ethnic cleansing".

Ms Suu Kyi has denied its security forces have been responsible for any serious rights violations and her government has blocked three UN investigators travelling to the country to further investigate.

- with agencies