Christmas decorations are not allowed on the streets of Aceh -- the only Indonesian province to implement strict Sharia law that includes punishments like flogging -- where 98 percent are Muslim and just 6,000 Catholics live.

The Sacred Heart Catholic Church, built almost 100 years ago by Dutch colonial rulers and the only one in the provincial capital Banda Aceh, was allowed to hold a ceremony Tuesday evening for a crowd of 500 faithful.

"I don't find any difficulty in terms of relationship with believers of other religions. So far, the religious tolerance here is excellent," the church's pastor, Father Agustinus Padang, told AFP.

Aceh has been widely criticised by rights groups for punishments of moral offences under the strict law, such as public canings for alleged adultery.

But the province's special autonomy excludes non-Muslims from those, and Catholicism is one of the nominally secular country's six official religions.

The church, located in the heart of the city and a stone's throw away from the grand mosque, is bare of any Christmas ornaments on its exterior.

A tight security presence of more than a dozen police and soldiers was also visible because of several attacks against Christians in Indonesia in recent years.

But inside the colonial-style church, worshippers celebrated with a tall Christmas tree, fairy lights, and a choir singing the Indonesian version of "Holy Night".

The sound of the Islamic call to prayer echoed around the church while preparations were underway for the Christmas celebration.

- 'Always feel safe' -

Catholics in the city prefer a muted celebration that focuses on self-reflection, so Christmas paraphernalia was only put up 24 hours before the big day, according to church administrator Baron Ferryson Pandiangan.

"Catholics in Banda Aceh assimilate well with other religions, despite the rules that Aceh must be managed with Islamic sharia law. It doesn't bother us at all," Pandiangan said.

Despite improvements in religious harmony, being a minority in the overwhelmingly Muslim region is not without challenges.

There are only 19 Catholic churches in Aceh, while Protestants have more than 180 churches.

Catholics mix with believers of other religions in Banda Aceh, partly bonded by the shared trauma of the devastating 2004 Boxing Day tsunami, which killed around 60,000 people in the city alone.

Their Sacred Heart church was affected by the giant waves, becoming flooded with thick mud while the initial earthquake destroyed parts of its walls.

Every year on December 26, the churchgoers congregate to mark the tragic event and pray for the victims.

While the Christmas celebration is less festive than in other parts of the world, worshippers still welcome the joy in the church that has become their little oasis.

"I always feel safe and comfortable to worship here because the security is tight," worshipper Lisbetty Purba told AFP.

The 35-year-old housewife said when she moved to Banda Aceh four years ago from neighbouring North Sumatra province, where many Christians live, she was worried about the rules she had to follow, but soon realised her worries were unfounded.

"I really love living here, I met good neighbours who are kind to me," she said.

"The key is communication and willingness to share."