In Indonesia's only province ruled by strict Islamic law, the sight of the "morals police" prompts women to quickly adjust their headscarves and male and female companions to move apart.

In Aceh on the northern tip of Sumatra island, it is the job of the 1,000-strong Wilayatul Hisbah, or Islamic police, to enforce sharia laws that mandate public modesty for women, and forbid unmarried couples from socialising.

In the capital Banda Aceh last week, a woman peeled away from her husband, reached for a scarf and quickly wrapped it around her head as a patrol approached; a petrified couple hopped on a motorcycle and fled.

But another pair hiding behind a large rock on the beach were not so lucky.

"Are you married?" roared a burly officer, wearing a khaki uniform and sporting a thick moustache, as he approached the cringing couple who shook their heads.

"This is unacceptable in Aceh, we have sharia laws here. Go along now, go home," he said, after examining their identity cards.

Because small violations earn usually no more than a reprimand, it is not uncommon to spot women without headscarves, or couples together in cafes or other public places.

Nevertheless Aceh, an autonomous region on the western edge of the scattered Indonesian archipelago, remains an anomaly in a country where most of the 240 million people practise a moderate form of Islam.

Alcohol is freely sold in the rest of Indonesia, the world's most populous Muslim-majority nation, but it is banned in Aceh. In some of the province's regions, women are forbidden from wearing tight trousers.

Gamblers and imbibers are publicly caned. Debate still churns in Aceh over whether adulterers should continue to be publicly flogged, or stoned to death.

In elections Monday to pick a governor and 17 district heads and deputies, voters will decide whether they want leaders who advocate stricter sharia laws.

They are Aceh's second polls since the province was devastated by a tsunami in 2004 that killed 170,000 people in the province and the end in 2005 of a 30-year separatist war against Indonesian rule that claimed 15,000 lives.

Incumbent governor Irwandi Yusuf, who supports sharia but rejects stricter laws including stoning, will face contenders such as Teungku Ahmad Tajuddin, a cleric who will not say outright whether he backs stiffer laws but opposes Yusuf for rejecting them.

The regular patrols by the Islamic police, which critics say infringe civil liberties, are embraced for the most part by the fervently religious population of five million.

"The sharia police are working for the good of Aceh and I support them," said Andara, a 27-year-old woman who works as a restaurant cashier, and like many Indonesians goes by one name.

"If nobody controls the people, they will do and wear as they please and what will happen to the Islamic sharia we have for so long defended?"

In this conservative outpost, children are educated about sharia laws in elementary school.

In December, 64 male and female punk-rock fans picked up at a concert in Banda Aceh were "morally rehabilitated" by the Islamic police -- they were forced to have their hair cut, bathe in a lake, change their clothes and pray.

Extreme views are rife in the province where there are no cinemas, music concerts are few, and billboards depict females in headscarves.

"Women who don't wear headscarves are inviting men to touch their breasts," said 47-year-old teacher Tarmizi Mohammad.

"I think we should enforce sharia laws further and stone adulterers and chop off the hands of thieves," he added.

But the morals police faced a setback in 2010 after two officers were jailed for gang-raping a woman in custody.

Sharia police chief Khalidin Loong said that recruitment regulations had been tightened since then, and defended stiff punishments. "The lashings are symbolic, to cause more shame than pain," he said.

Not everyone in the province likes the sharia police, however, and some refuse to live according to sharia law -- even if it gets them into trouble.

"People called me a dog, the bringer of disasters, the inviter of the next tsunami. I have been picked up by the sharia police many times," said 20-year-old student Dila, who defiantly walks around in miniskirts and without a headscarf.

Wearing a T-shirt and jeans, and without a headscarf, 22-year-old Dia Fatiya said the people of Aceh accepted the way she dressed and it was only the sharia police that protested.

"The Acehnese people have become more open-minded and they never fuss over whether I am dressed properly or not," she said.

"I dislike the sharia police. I hope they will disappear," she added, between puffs on a cigarette at a cafe.