As Muslim hardliners in Jakarta plan a mass protest on Friday, the city is on high alert.

The metropolitan police has mobilised about 7,000 officers, who will be backed by an additional 500 troops from the Indonesian military (TNI), to secure the city and to prevent any outbreak of violence during the gubernatorial elections which began last Friday.

The protest was triggered by criticisms by Jakarta governor Basuki Tjahaja Purnama of his opponents who cited a verse from the Quran to attack him previously.

National police chief Tito Karnavian confirmed that he has raised the security alert level in Jakarta to its highest as thousands of demonstrators are expected to arrive from outside the city on Friday to join Muslims to protest against Basuki for allegedly insulting Islam.

A TNI spokesman also said that the military has received a tip-off that the protest may escalate into violence and hence soldiers have been deployed to support the police.

President Joko Widodo said in a statement on Monday that while public demonstration is a democratic right of citizens, those rights do not include them being allowed to impose their will and damage public property.

"The government will guarantee the right to free speech but also will give priority to public order," said Mr Joko.

"I have prepared our security forces and they are ready to perform their duties in a professional manner if anyone commits anarchy."

Basuki, or Ahok, as he prefers to be called, is currently on leave to take part in the ongoing campaign and has since apologised for his remarks, even subjecting himself to police questioning over the incident.

But that did not stop what some have estimated to be about 10,000 Muslim hardliners from staging a mass protest outside City Hall two weeks ago.

The authorities are anticipating that more will show up at the second demonstration, planned after Friday prayers this week, including many who will travel into the city from elsewhere, including nearby Bekasi or Tangerang.

Ahok's no-nonsense approach in running Jakarta has made him a popular choice to be re-elected but being ethnic Chinese and Christian has made him a target of critics who say he is not suitable to govern the capital of the world's most populous Muslim-majority nation.

But many political watchers say those issues are unlikely to derail his bid for re-election, citing a recent survey released by pollster Saiful Mujani which indicated that the majority of Jakarta voters are "moderate" and do not consider religion and ethnicity as important factors in deciding who to vote for.

Still, some experts have said that the issue of race and religion will threaten to turn the gubernatorial election into a test of religious tolerance in Indonesia.

A handful of Islamic groups in and outside of Jakarta have called for Muslims to rally behind the protestors in the capital, reported The Jakarta Post on Monday.

These include Islam Defenders Front (FPI) chairman Habib Rizieq Shihab, who has called on all Muslims to take part in the rally. There are, however, other organisations such as Indonesia's largest Islamic group, the Nahdlatul Ulama (NU), which has discouraged its members from taking part in the demonstration.

It has also prohibited the use of its symbols at the upcoming rally. NU has also said that it suspects the demonstration carries a "hidden" aim that is "bigger than demanding criminal proceedings against Ahok," reported The Jakarta Post.

"I am afraid that (the rally) is propelled by a third party whose issues are bigger than just the (Jakarta) election," said NU central board chairman Said Aqil Siradj on Saturday. --BERNAMA