A series of bomb blasts have rocked the Indonesian capital, Jakarta, followed by gun battles on the streets.
The blasts were centred around Thamrin Street, a major shopping and business district close to embassies and the United Nations offices.
Police say four suspected attackers are among at least six people killed. It is not yet clear what group was behind the assault.
President Joko Widodo has called for calm but condemned the “act of terror”.
“We all are grieving for the fallen victims of this incident, but we also condemn the act that has disturbed the security and peace and spread terror among our people,” he said.
Images from Jakarta have showed several bodies lying on the road outside a cafe, as well as seriously injured people being carried away.
Details remain unclear, but at least one of the blasts hit a Starbucks cafe outside the Sarinah shopping centre and next to a police security post.
Eyewitnesses say several attackers entered the cafe and detonated explosives.
Gunfire broke out after police arrived at the scene and there were several further explosions and reports of police chasing suspects.
Armed police, snipers and armoured vehicles were deployed on the streets of the capital.
BBC Indonesian reporter, Jerome Wirawan said police cordoned off the area around the shopping centre.
A UN official, Jeremy Douglas, told the BBC he was about 150m away from one of the first blasts near the UN’s building.
“Then we ran into the building. We heard a third explosion. We got up to our office on the tenth floor and we heard a fourth, a fifth and a sixth.”
A few hours later, police said four attackers had been killed.
National Police Deputy Chief Commander Gen Budi Gunawan said two had been killed in a shootout outside a theatre and two others blew themselves up at the police post in front of Starbucks.
Indonesia has been attacked by Islamist militant groups in the past and was on high alert over the new year period after threats from the so-called Islamic State (IS).
National police spokesman Anton Charliyan said while it was not yet clear who carried out the attack, IS had warned of a “concert in Indonesia” which would be international news.
Jakarta police have been saying for some time that an attack on Indonesian soil may be just a matter of time.
Although it isn’t yet clear who is behind these attacks, they appear designed to inflict maximum damage.
Although no-one has claimed responsibility for these attacks, in the last few years there have been anywhere between 150-200 Indonesians who it is thought have gone to Syria to fight with IS.
Many have since returned and the police have thought that they might be preparing an attack in Indonesia.
Indonesia is the world’s most populous Muslim nation but by and large is secular, although in recent years the threat of radicalism has remained high as small networks of militants are still thought to be operating in the country.