At least five children drowned when boats carrying Rohingya refugees fleeing violence in Myanmar sank early on Wednesday, Bangladesh border guards told AFP.

Authorities said three to four boats had sunk at the mouth of the Naf river, which divides Bangladesh and Myanmar's violence-wracked Rakhine state, raising fears there could be many more casualties.

Scores of people have already been killed attempting to cross the Naf border river since a fresh upsurge in violence in Rakhine on August 25, many using small fishing boats unsuited to the rough coastal waters.

Border Guard Bangladesh officer Aloysius Sangma said three to four boats packed with Rohingya refugees had gone down early Wednesday. “So far, the bodies of five male and female children have been found at different locations,” he told AFP.

Local police chief Main Uddin said authorities were travelling to the spot to investigate. More than 125,000 refugees have flooded across the border into Bangladesh.

Most are Rohingya, a Muslim ethnic minority that the government of Buddhist-majority Myanmar largely does not recognise as citizens.

UN chief urges Myanmar to give legal status to Muslims

UN Secretary General Antonio Guterres has called for the Muslims of Myanmar's troubled Rakhine state to be given either nationality or legal status, and voiced concern about violence that has since late August forced nearly 125,000 people to flee and risk destabilising the region.

“I have condemned the recent attacks by the Arakan Rohingya Salvation Army. But now we are receiving constant reports of violence by Myanmar's security forces, including indiscriminate attacks,” the secretary General told reporters in New York, expressing concern about the security, humanitarian and human rights situation in Rakhine.

“This will only further increase radicalisation.”

Guterres said that he has officially written to the Security Council to express his concern and to propose various steps to end the violence, adding that the grievances of Rohingya Muslims in the Rakhine state “have festered for far too long and are becoming an undeniable factor in regional destabilisation.”

He called on the international community to prevent further escalation and to seek a holistic solution and urged the authorities in Myanmar to provide security and aid to those in need and safe access to life-saving aid.

“At the same time, it is no longer possible to delay an effective action plan to address the root causes of the crisis,” the secretary general said.

“It will be crucial to give the Muslims of Rakhine state either nationality or, at least for now, a legal status that will allow them to have a normal life, including freedom of movement and access to labour markets, education and health services.”