Myanmar said Saturday that Muslims would not be allowed to register as "Rohingya" in its first census in three decades despite UN assurances, on the eve of a survey that has fanned sectarian tensions.

The move came as Buddhists in an unrest-hit western state vowed to boycott the census over fears it could lead to official recognition for the Rohingya, viewed by the United Nations as among the world's most persecuted minorities.

"If a household wants to identify themselves as 'Rohingya', we will not register it," government spokesman Ye Htut told reporters in Yangon.

He said people could call themselves "Bengali", a term used by the authorities who view most Rohingya as illegal immigrants from neighbouring Bangladesh.

Foreign aid workers fled the restive western state of Rakhine this week after Buddhist mobs attacked their offices as tensions escalated in the run up to the census.

An 11-year-old girl was killed by a stray bullet after police fired warning shots to disperse angry crowds in the state capital Sittwe.

Humanitarian workers in the region have come under increasing pressure from Buddhist nationalists who accuse them of bias in favour of local Muslims.

The United Nations is pulling some 50 international and Myanmar staff from the region, while other major humanitarian groups are also removing their workers temporarily.

Households across Sittwe were seen Saturday bearing signs declaring: "This house is protesting against the census. Do not register".

Myanmar's first census since 1983, which is set to begin on Sunday and last for 12 days, is backed by the United Nations Population Fund (UNFPA) and is aimed at plugging an information deficit in the former junta-run country.

The population tally has come under fire for its inclusion of ethnic and religious questions, which critics say will further fan the flames of unrest and threaten fragile peace talks with minority rebel groups.

Buddhist nationalists have reacted with fury to the fact that the questionnaire includes a section for people to self-identify their ethnicity, theoretically allowing the Rohingya to be registered as such and raising fears it could lead to political rights for the group.

But government officials in the state have sought to assure them that the term will not be counted, according to local MP Aung Mya Kyaw.

"They will only write down 'Bengali' because Rohingya doesn't exist," he told AFP.

Long-standing animosity between Buddhists and Muslims in Rakhine erupted into bloodshed in 2012, leaving dozens dead in clashes and around 140,000 people displaced.

Muslims in remote parts of Rakhine have reported that the authorities have threatened local people with harsh penalties if they try to identify as Rohingya.

The Rohingya are subject to a web of restrictions on travel, work and even marriage.