Several explosions have been heard in the center of Jakarta, media reports say, and at least one location police engaged gunmen in a firefight.
CNN affiliate CNN Indonesia reported that a police station appears to have been the target of the attacks.
Amateur video, posted on Twitter, appears to have caught one of the explosions outside a coffee shop in the Sarinah area.
Police have confirmed to CNN that there were four fatalities, one policeman and three civilians. It is not confirmed if the dead civilians are the attackers.
There are reports that there have been several explosions, at least one at a police station at a busy intersection in central Jakarta.
Police spokesman Anton Charliyan told CNN that a number of grenades were used in the attack.
No buildings around the police station appeared to have been damaged.
Authorities were in pursuit of at least one attacker who escaped from the scene and is probably armed. There have so far been no claims of responsibility and police have not named any suspects.
There is a U.N. building in the vicinity, at the end of the central business district, near the presidential palace.
The country has been on high alert in recent weeks, with the police and military joint operations, focused on hitting the East Indonesian Mujahadeen, which has pledged support for ISIS.