Thousands of people have marched in protest in Indonesia after police said they are to investigate a complaint of blasphemy against the Christian governor of Jakarta.

Basuki Tjahaja Purnama, who is known as Ahok, is an an ethnic Chinese Christian and the 10,000 protestors called for tolerance and unity in the face of demand from hard-line Muslims that he be prosecuted for blasphemy.

Press in Jakarta reported that police chief Tito Karnavian considered long and hard before deciding to pursue the case.

Indonesia is a secular state but has the largest number of Muslims of any country in the world, more than 200 million. Nearly all are Sunni. Blasphemy is a criminal offence and dozens of people have been convicted in the last decade, some sent to prison for as long as five years.

Hard-line Muslims in Indonesia first reported Purnama to police for alleged blasphemy on 6 October.

"Police are preparing a file to the prosecutor and the court," said Karnavian, adding that not to proceed would have risked serious protests across Indonesia. 

Already there has been disruption on the streets. In one protest earlier this month, more than 100,000 Muslims took to the streets, leading to one death and dozens of injuries. Purnama, who has not been arrested but has been prohibited from leaving Indonesia, is up for re-election next February.

He is a social reformer who has cracked down on corruption, and is alleged to have delivered a speech in September when he accused his rivals of using the Qur'an to deceive voters. This speech was then posted online, where his words were edited to make it look as though he was directly criticising the Islamic holy book. The Islamic Defenders Front, a hard-line group that campaigns for Sharia law, demanded his arrest.

Purnama told journalists: "I accept the status of suspect and believe in the professionalism of the police. This is not just a case about me but about determining the direction this country is going in."

Johan Budi, a spokesman for the president, Joko Widodo, said the police decision must be respected.

He said: "From the beginning, the president has said he would not intervene."

Additional reporting by Reuters.