Terrified residents were fleeing northern Myanmar on Friday, thousands leaving on foot and others airlifted out by helicopter, as troops hunted through torched villages for those behind attacks on police that have raised fears Rakhine state could again be torn apart.

Local officials believe hundreds of people from the area, home to many from the persecuted Muslim Rohingya minority, spent months planning attacks on police posts along the Bangladesh border that sparked the crisis this week.

Dozens of people have died in an ensuing military lockdown, sparking fears of a repeat of 2012 when sectarian clashes ripped through Rakhine leaving more than 100 dead and driving tens of thousands into displacement camps.

Troops and police have repelled multiple onslaughts on a security office by 50 "violent attackers" and captured a fifth suspect, state media reported on Friday.

Meanwhile families have streamed down the roads around Maungdaw town on foot, their worldly possessions stuffed into carrier bags and plastic buckets or strapped to the front of bicycle rickshaws.

Around 180 teachers, workers and residents were also airlifted out of the region at the epicentre of the crisis, while hundreds of government staff have poured into the state capital Sittwe.

On the ground in Maungdaw, an AFP journalist reported seeing clouds of smoke billowing from a village Thursday near charred remains of two dozen bamboo houses that the military said "terrorists" had torched the previous day.

Troops have killed 26 people since deadly raids on border posts Sunday, according to state media. Nine police died that night, and four more soldiers have lost their lives in ensuing clashes.

Witnesses say troops used Sunday's attacks as an excuse for a crackdown against them, gunning down unarmed Muslim civilians in the street. The military say they have been defending themselves from armed attackers.

Most residents in northern Rakhine are Rohingya, a stateless minority branded illegal immigrants from Bangladesh by many from Myanmar's Buddhist majority.

- Killings, burnings, arbitrary arrests -
The Organisation of Islamic Cooperation issued a statement calling for calm, after receiving "disturbing reports of extra-judicial killings of Rohingya Muslims, burning of houses, and arbitrary arrests by security forces".

Rakhine state government spokesman Min Aung said the border post assailants had spent months plotting the raids, which were originally intended to hit as many as seven targets.

"There are about 200 to 300 currently in the group," he told reporters in Sittwe, declining to explain how he knew.

"According to our interrogations of those we have arrested, they initially planned to attack six or seven locations."

Authorities have given scant details of who was behind the assaults, though officials have publicly pointed the finger at Rohingya insurgents and privately blamed Bangladeshi groups across the border.

The military said late Thursday troops had captured a fifth suspect, along with a gun, ammunition and flags featuring the logo of the RSO, a Rohingya militant group founded in the 80s and long considered defunct.

The RSO vigorously denied the accusations in a message to AFP. Attempts to contact the sender went unanswered.

Videos showing armed men speaking the Rohingya language calling for jihad that have been circulating on social media -- which analysts said appeared to be genuine -- have raised concerns a new local militant group may have emerged.

The escalating unrest in Rakhine poses a major challenge for the country's new elected government, led by democracy champion Aung San Suu Kyi.

The Nobel laureate has faced international criticism for not doing more to help the Rohingya, and on Wednesday she vowed to follow the rule of law when investigating the border guard attacks.