Indonesian police are planning a massive show of force in the capital Jakarta to contain a much-hyped protest by Muslim hardliners against the city's popular governor that threatens to ignite religious and racial flashpoints.

An accusation of blasphemy against the Jakarta governor Basuki “Ahok” Tjahaja Purnama, an ethnic Chinese and minority Christian who is an ally of the country's president, has galvanized his political opponents in the Muslim-majority nation of 250 million and given a notorious group of hardliners a national stage.

National Police spokesman Boy Rafli Amar said 16,000 police will be deployed along with 2,000 soldiers and 2,000 of Jakarta's public order officers for the protest that is expected to begin in the early afternoon following prayers.

Gen Gatot Nurmantyo, chief of Indonesia's powerful military, has said it “will be in the frontline against any movement aimed at disrupting the unity and integrity of the nation.” 

Indonesians are already fighting on social media over the blasphemy claim and the protest, which organizers optimistically boast will attract half a million people to Jakarta's traffic clogged streets. Police have said it might draw up to 100,000 people based on communications with Muslim groups involved in its planning.

Blasphemy is a criminal offence in Indonesia and prosecutions have increased in the past decade. Amnesty International documented 106 convictions between 2004 and 2014 with some individuals imprisoned for up to five years.

Ahok, who is seeking a second term as Jakarta governor and is a possible running mate for President Joko “Jokowi” Widodo in the 2019 presidential elections, is popular with Jakarta's middle class. He is adored as a blunt speaker who doesn't tolerate corruption and articulates a vision to make the chaotic, dysfunctional city more like clean, orderly and efficient Singapore.

But the anti-corruption stance has made him enemies and the evictions of thousands of the city's poorest people to make way for urban improvement has stoked anger and resentment and played to a stereotype of Chinese as exploiters of Indonesia's poor Muslim masses.

On the national stage, Ahok is ranged against former President Susilo Bambang Yudhoyono, whose son is a candidate for Jakarta governor, a role that is a stepping stone to national leadership.