At least 18,500 Rohingya have crossed into Bangladesh since fighting erupted in Myanmar's neighbouring Rakhine state six days ago, the International Organization for Migration said Wednesday.

Plumes of smoke billowed from several burning villages in the worst-hit section of the state, according to an AFP reporter on a government-led trip to the area, as the violence showed little sign of abating despite security sweeps by Myanmar's police and troops.

The streets of Maungdaw -- northern Rakhine's largest town -- were virtually deserted as fires flickered among charred remains of houses and the occasional burst of gunfire echoed in the distance.

The clashes began on Friday after militants from Myanmar's Rohingya Muslim minority community staged deadly surprise raids on police posts.

At least 110 people, including 11 state officials, have been confirmed dead and thousands of Rohingya have poured across the border to Bangladesh despite Dhaka's attempts to stop them.

"As of last night, 18,500 people have come across," Chris Lom, the IOM's Asia-Pacific spokesman, told AFP, adding an unknown number were still stuck on the Myanmar side of the border.

An estimated 6,000 Rohingya on Tuesday massed at the "zero line" border with Bangladesh, days after the area came under mortar and machine gun fire by Myanmar security forces.

The Rohingya, the world's largest stateless minority and subject to severe restrictions on their movements, are barred from officially crossing.

Bangladeshi authorities on Wednesday toughened patrols in a bid to prevent more arrivals in a country that already hosts an estimated 400,000 Rohingya, albeit in abject conditions.

Rohingya have sneaked across the land border in large number or swum the Naf River which marks part of the frontier.

But tragedy befell some of them. The bodies of two Rohingya women and two children washed up on Bangladeshi soil on Wednesday, an official there told AFP, drowned after their rickety boat capsized.

- Fight and flight -

Among the dead and displaced are also ethnic Rakhine Buddhists and other tribal groups, who say they are being targeted by Rohingya militants.

Five ethnic Buddhist men were found stabbed to death early Wednesday in Maungdaw, which is under curfew, Ye Htut, the town's district chief told AFP.

With information trickling out, a picture has emerged of a cat-and-mouse game between militants and security forces played out in remote hamlets, fields and forest hideouts.

The office of de facto leader Aung San Suu Kyi said militants have repeatedly detonated homemade explosives and attempted to firebomb police posts and ambush patrols.

Myanmar classes the militants as "Bengali terrorists" and blames them for setting fire to both their own and other community's houses.

Rohingya arriving in Bangladesh have told a different story, saying their homes had been set on fire by security forces and Buddhist mobs.

"Villagers are running away... where do we have to live now?" one Rohingya from a village near Maungdaw told AFP by phone, speaking on condition of anonymity.

It was not immediately possible to verify his account.

- Maximum restraint? -

Rakhine has been beset by religious violence since 2012.

Analysts say the emergence of organised militancy is a game-changer in an already volatile situation.

Displaced Rohingya reaching Bangladesh have told AFP some men are heeding a call to arms by the militants and staying behind to fight in their villages.

The Arakan Rohingya Solidarity Army (ARSA) claims its men launched Friday's surprise attacks on police posts, killing 11 state officials, with knives, homemade explosives and a few guns.

After years in which the Rohingya largely avoided violence, the group emerged last October to carry out deadly attacks on police posts.

That prompted a months-long security crackdown by Myanmar's army which left scores dead and forced 87,000 people to flee to Bangladesh.

The UN believes those operations may have amounted to ethnic cleansing of the Rohingya -- allegations denied by the army.

On Sunday Pope Francis led mounting international calls for the protection of "our Rohingya brothers".

The UN has also urged Myanmar to protect civilians during its operations and called on Bangladesh to allow the displaced into its territory.

With pressure mounting, a Myanmar government official on Tuesday said security forces would use "maximum restraint" in coming days but insisted on the country's right to defend itself from "terrorists".

Rights groups say the reports of Rohingya villages being torched fit the counter-insurgency playbook of Myanmar's army.

"These are the sort of tactics we've seen before," said Phil Robertson of Human Rights Watch.