The Christian governor of Jakarta has been named as a suspect in a case of alleged blasphemy.

Basuki "Ahok" Tjahaja Purnama caused outrage in the capital of the world's most populous Muslim nation when he was accused of insulting the Qur'an. Purnama, popularly called "Ahok", is a Christian from a Chinese ethnic group and the case is seen as a test for Indonesia's commitment to religious freedom.

The police announcement came after mounting pressure and mass protests from religious hardliners who demanded the politician be arrested and charged.

"Police have decided to declare Basuki Tjahaja Purnama a suspect and bar him from travelling abroad," national police chief detective Ari Dono Sukmanto said on Wednesday morning.

"After long discussions, we reached a decision that the case should be tried in an open court," he added.

The naming of Purnama means prosecutors can bring him to trial and if found guilty he will face up to five years in prison.

He is accused of blasphemy after he cited the Al Maidah 51 verse in a campaign speech and said it had been used to deceive voters into thinking Muslims should not be led by non-Muslims.

He later apologised and said he had not meant to cause offence.

But an altered version of his comments made to seem more extreme and offensive was circulated online, according to the Guardian, prompting a mass demonstration in Jakarta demanding his arrest.

The protests have since taken an anti-Chinese dimension with tensions between Indonesia and China an ever-present reality.

Purnama is not barred from the February election to be re-elected governor and said he would still part in the campaign.

But a human rights expert has said now that he has been named as a suspect by police, it will be difficult for him to escape prosecution.

"I have studied more than 200 blasphemy cases in Indonesia since it was written by President Sukarno in 1965. Over this 50-year period I think there was only one case where the suspect was acquitted," Andreas Harsono from Human Rights Watch told the Guardian. "I don't think Ahok can survive this prosecution, he is very likely to end up in jail."

He added: "I think it is going to be difficult for Ahok to defend himself. Why? This is a law, in Bahasa Indonesia, we call it pasal karet, a rubber article. It is always political."