There was no immediate claim of responsibility for the rattle of shots and explosions from at least five attackers. But police believe that they were linked to ISIS, and the Islamic State-affiliated Aamaq News Agency reported people from that terror group were behind the bloodshed.
The Jakarta carnage, in an area frequented by foreigners, came 6,000 miles from and two days after ISIS boasted about a suicide bombing in the heart of Istanbul. That attack in Sultanahmet Square, between the popular Hagia Sophia and Blue Mosque tourist attractions, killed 10 German visitors.
CNN security analyst Bob Baer likened the Jakarta attack to the November 13 Paris massacre in which terrorists linked to ISIS struck several locations at the same time. Yet the number of dead was nowhere near the toll of 130 in France, with Clarke Jones, a counterterrorism expert at Australian National University, calling it "fairly amateurish ... with hand grenades and firearms."
Another expert, Sajjan Gohel of the Asia-Pacific Foundation think tank, said it was particularly worrisome that this happened in the capital of Indonesia.
It was the first major attack in Jakarta since the 2009 simultaneous attacks on the J.W. Marriott and Ritz Carlton hotels, which left seven people dead. Since then, the secular government has made major inroads beating back terror groups in an Asian nation where about 87% of its roughly 255 million people are Muslim.
"It's concerning (to have) yet one more day and another attack in another part of the world," Gohel told CNN. "And one fears that this is potentially becoming the new normal where ISIS affiliates carry out attacks independently from the leadership based in Syria."
'We were so scared'
It began around 10:55 a.m. Thursday (10:55 p.m. ET Wednesday) with a suicide explosion inside a Starbucks on Thamrin Street, an entertainment and shopping district with various Western chain restaurants and stores.
That set in motion two others outside the coffee shop to seize two foreigners, eventually dragging them into a parking lot and shooting them, said Jakarta police spokesman Anton Charliyan. They also opened fire at people on the street.
Heavily armed police soon swarmed the scene, firing on the militants and looking for other attackers.
The attackers responded by firing back and tossing two grenades at the officers, according to Charliyan. Minutes later, two more rode a motorcycle toward a nearby police post and blew themselves up.
Christian Hubel told CNN that he and his colleagues heard five or six explosions, one after the other. And Handi Kurniawan, who watched everything unfold from his office 20 floors above, called the ordeal "horrible."
"We were so scared," Kurniawan told CNN. "We just could not believe that this kind of thing (could) happen again in Jakarta."
Dutch national among 19 wounded
The blasts and gunshots stopped by Thursday afternoon. And by nighttime, authorities were no longer hunting for attackers -- though they are looking for those who helped them in plotting, financing and getting weaponry, according to Charliyan, the police spokesman.
By then, police had already counted five assailants dead at the scene. There was conflicting information about the victims, with some officials putting the number of dead as high as six.
Charliyan said it's believed the attackers were affiliated with ISIS and were targeting police and foreigners -- the latter also being a presumed motive in the Istanbul attack and the 2009 Jakarta blast.
At least one foreign national is among the dead, authorities said. Charliyan said 19 people, including at least one more foreigner, were wounded.
Angele Samura, the security adviser for the Netherlands Embassy in Jakarta, said a Dutch national underwent surgery after being "severely injured." It's not known if this is the same Dutch citizen and U.N. Environment Programme worker who that agency reported was hurt.
A new explosion was heard around 9 p.m. from the top of a building near where the other attacks occurred 10 hours earlier. But details were not immediately clear -- including whether it was a controlled blast, if anyone was hurt or killed or how it was set off.
Worries about ISIS fighters returning home
Jeremy Douglas, who works in the United Nations Office on Drugs and Crime in the area, said the location suggests if the terrorists "wanted to make an impact and get visibility ... this is the place to do it."
"You couldn't get much more central in Jakarta if you tried," Douglas said. "It's basically right smack dab in the central business area."
In recent weeks, Indonesian police have been on high alert, while military operations focus on hitting the East Indonesian Mujahadeen, helmed by Indonesia's most-wanted terrorist, Santoso, who has pledged support for ISIS.
One major worry is that Indonesians fighting in Syria and Iraq will return home, having gained training and combat experience.
Yet many in the country acted more defiant than anything in the aftermath of Thursday's attacks. Many went on Facebook and Twitter using #KamiTidakTakut -- which translates to "We are not afraid" -- to express their pride and conviction to stand up, rather than bow down, to terrorism.
"We are Indonesians & we never affraid to terrorist," one man wrote. "We always fight anything that wanna take us down."
This sentiment was echoed by President Joko Widodo.
"We should not be afraid and defeated by acts of terror like this," he said.