Hundreds of supporters of Jakarta's Christian governor sang patriotic songs outside the Indonesian capital's City Hall on Wednesday to protest his imprisonment for blasphemy after a trial that drew concerns over rising religious intolerance.

Governor Basuki Tjahaja Purnama is appealing his harsher-than-expected two-year jail sentence after being found guilty of insulting the Koran in the Muslim-majority country.

Purnama, the first ethnic Chinese and Christian leader to be elected as Jakarta's governor, was immediately detained, on the judge's orders, at the end of the trial on Tuesday.

While he was held in a police detention facility on Jakarta's outskirts, Purnama's supporters dressed in the national colors of red and white to gather at his office in a show of solidarity at the Dutch colonial-style City Hall.

The emotions unleashed by the case have sent shudders through Indonesia - a secular state that has religious freedom and diversity enshrined in the constitution, though 85 percent of its people are Muslim.

A Hindu spiritual leader from the holiday island of Bali, I Gusti Ngurah Harta, said Purnama's guilty verdict meant minorities could be disadvantaged before the law in the future.

"It means that before the law, minorities will be increasingly oppressed because judges can't do much in the face of the pressures they face," he said.

Rights groups have condemned the verdict.

They fear Islamist hardliners are in the ascendancy in a country where most Muslims practise a moderate form of Islam and is home to sizeable communities of Hindus, Christians, Buddhists, and people who adhere to traditional beliefs.

Purnama, who is an ally of President Joko Widodo, was put on trial late last year over allegations that he had insulted the Koran when he said political rivals were deceiving people by using a verse in from the Islamic holy book to say Muslims should not be led by a non-Muslim.

Islamist groups drew hundreds of thousands of protesters onto the street, calling for him to be sacked and jailed, scuppering his chances at re-election.

Though he remains popular for his record of getting things done, Purnama lost April's divisive election to a Muslim rival who will take office in October.

At Jakarta's City Hall, Purnama's supporters worried about healing the divisions caused by the election and trial.

"Look at the situation with consideration for the Unitary State of Indonesia, not for the hatred toward a group, religion or certain people," said Hironimus Rupa, a 36-year-old Catholic priest who had joined Purnama's supporters.

An umbrella organization for Islamic groups that led the anti-Purnama protests called on Wednesday for all sides to "understand and accept the judge's decision."

Purnama, considered a "double minority" because of his ethnicity and religion, has received an outpouring of sympathy from across the archipelago nation and internationally.

"I admire his work for Jakarta. Don’t believe he’s anti-Islam. My prayers are with his family. Leaders must safeguard tolerance and harmony,” Moazzam Malik, Britain's ambassador to Indonesia, tweeted after the verdict.

A Christian activist in the eastern-most province of Papua said Purnama had been treated unfairly.

"It clearly shows that this country does not respect diversity and the people of Papua feel (Purnama) has been tyrannized," said Victor Mambor.