Aleppo (Syria) (AFP) - Tens of thousands of Christians have fled Syria's war-wracked second city Aleppo but many others are determined to hold out despite their dread of Islamic State jihadists.

Christians of various denominations make up around 10 percent of Syria's population, and Aleppo alone was home to some 250,000 before the civil war reached the city in 2012.

In the Orthodox church of Mar Elias, the golden-robed deacon blesses his dwindling congregation of around 100 with incense as the choir muffles out nearby bombardment.

Families from government-controlled districts gather every Sunday evening in the church, which is brightly lit thanks to its generator, a major draw in a city where frequent power cuts plunge homes into darkness.

"A lot of members of our community have left because they lost their jobs and because of terror of Daesh," said Georges Bakhache, public relations officer for Aleppo's Christians, using the Arabic acronym for IS.

"The jihadists are not in town but they're not far," he said.

"Christians panicked when they saw what happened to the Christians of Mosul," Iraq's second city which IS seized in June, he added.

"They were given the choice of converting, paying jizya (a tax levied on non-Muslims by pre-modern Islamic states and revived by IS) or fleeing. Almost all of them picked the last option.

"That caused a big stir here and Christians left for Lebanon, Sweden, Canada, America and Armenia."

The northern metropolis of Aleppo, which was the economic hub of pre-war Syria, has since July 2012 been split into a western sector controlled by government troops and a rebel-held east.

IS has fighters in parts of Aleppo province east of the city.

Bakhache says he is determined to stay put, rather than join his brothers and parents living in the safety of the United States.

"Despite it all, we will not leave our land. Impossible," he said, clutching his two-year-old son in his arms.

An exodus -- of both Christians and Muslims -- started when Syria's civil war descended on Aleppo two years ago.

According to Fabrice Balanche, a French university lecturer and specialist on Syria, only around one million residents remain out of the city's pre-war population of 2.5 million.

Of its 250,000 Christians, "more than half have left, and there are only 100,000 left, 50,000 of them Armenians," said Balanche.

Basile Shawa, who runs a coffee shop behind Mar Elias, is confident they will return.

"Many Christians who emigrated insist their exile is only temporary, that they'll come back to the country once the situation improves and there's work," he said.

- Ready for Christmas -

Father Imad Daher of the Latin church of Saint Francis said Christians are preparing to put up their Christmas trees.

"We will celebrate Christmas, even if our numbers have dwindled. We will celebrate with a mass for peace," he said.

"We will decorate the Christmas trees in church and in homes," but not outside, "out of respect for the martyrs, because a lot of blood has been spilt."

Father Imad, who was badly wounded when a shell crashed into the city's Church of the Dormition on October 10, 2012, said Aleppo's Christians would never give up.

"We will still be here 100 years from now because this is our land," he said.

The cleric lost an eye in the shelling and now has a prosthetic cheek as well as an iron rod with screws in his arm.

"I was treated in Lebanon and then came back, because a shepherd does not abandon his flock, otherwise the wolf will come," he said.

The eight different Christian communities of Aleppo are now clustered in six government-run neighbourhoods, while around 100 are left "on the other side" in the Kurdish district of Sheikh Maqsud and a handful in rebel-held Jdaideh.

At the area's Saint Elias centre for the elderly, only six residents remain. Families came and moved the others to western Aleppo and "they never returned", said its director Abu Yussef.