At least 17 people have been killed in a series of bomb and gun attacks in central Jakarta, Indonesia's police told Al Jazeera, as gunfire rang out of the capital's downtown area.
An unknown number of people were injured in the security operations at the Sarinah shopping complex on Thamrin Street in the centre of Jakarta on Thursday.
At least five gunmen were among the dead and another five policemen and seven civilians were killed, police told Al Jazeera.
All six blasts occurred about 50 metres apart in the central business district, which also houses a United Nations office.
A Dutch national, who was working for the UN, was severely injured, Dutch media reported. Earlier reports said the man had died in the attacks. 
Tweets from the account of Jeremy Douglas, regional representative of the UN office on Drugs and Crime for Southeast Asia and the Pacific, described a bomb and "serious" exchanges of gunfire on the street outside his office.
Al Jazeera's Step Vaessen, reporting from Jakarta, said a police post was destroyed in a grenade blast and that sporadic gunfire was heard in the downtown area of the capital.
"Six gunmen on motorbikes entered the downtown area carrying long rifles, shooting into the crowd, with some carrying explosives," Vaessen said. "One of the gunman shot a police officer from close range."
Some gunmen on motorbikes reportedly escaped, police sources told Al Jazeera.
"Witnesses told Al Jazeera that they found nails on the streets near the affected area, indicating that the fragments came from the explosives used in the attacks," Vaessen said.  
The attacks caused panic in Jakarta's downtown area and prompted a security lockdown and enhanced checks in several areas in the crowded city of 10 million.
"The police are still investigating so we don't know how and why the attack happened. There were at least six explosions, and so far it looks like the police was the target," our correspondent said. 
An Indonesian policeman runs near the site of a blast in Jakarta [Beawiharta/Reuters]
A witness told Al Jazeera that one of the gunmen shot a police officer from close range. 
'Credible threat'
The deadly attacks were not a complete surprise to Indonesian authorities, who warned last month of a credible threat.
The government had deployed 150,000 security personnel to safeguard churches, airports and other public places across the nation, and made a series of pre-emptive arrests.
A series of arrests accompanied the warnings, as Indonesian police said they foiled a plot to kill government officials, law enforcement officers and others.
The heightened security extended through Christmas and New Year's before ending January 6.
It's unclear whether Thursday's attacks were related to the earlier reported threat. No one has claimed responsibility for the attacks.
However, police have confirmed to Al Jazeera that the Islamic State of Iraq and the Levant (ISIL) group had made specific threats towards targets in Indonesia recently.
Indonesia, the world's most populous Muslim nation, has been a victim of several bombing attacks in the past, claimed by Islamic groups.
Thursday's attacks, however, were the first major incidents in Indonesia's capital since the 2009 bombings of two hotels that killed seven people and injured more than 50. 
Presidential statement
Indonesian President Joko "Jokowi" Widodo, who was on a working visit in West Java town of Cirebon, has ordered security forces to hunt down the perpetrators and their network behind the attacks.
"I have received reports some time ago about the explosion in Thamrin street Jakarta. We express condolence to those who became victims, but we all also condemn the attack that caused restless among the community," Jokowi said.
He said he had ordered the national police chief and the minister for political and security affairs to hunt down and capture the perpetrators and those in their network. Jokowi said he was cutting short his visit and retuning to the capital.
"This act is clearly aimed at disturbing public order and spreading terror among people," Jokowi said in statement on television.
The attacks come two days after jailed Islamic leader Abu Bakar Bashir appealed to a court to have his conviction for funding a "terrorist training camp" overturned.
The 77-year-old leader of the Jemaah Islamiyah network filed a judicial review of his 2011 conviction, when he was sentenced to 15 years in jail for setting up the camp in Aceh province. A higher court later cut the sentence to nine years.
The attacks in the Sarinah area in downtown Jakarta als damaged a Starbucks [Al Jazeera]
Police were deployed near the site where one explosion went off, as local media reported more blasts in other parts of the city [Dita Alangkara/AP]