The 8 a.m. explosion in the San Andresito shopping area was the first to hit the Colombian capital since another car bomb blew apart an exclusive social and sports club eight months ago, killing 36 people and injuring 160 others.
Leftist rebels were accused of setting off the earlier bomb, but authorities were not so quick to assign blame for Wednesday's attack, which may have been carried out by criminals.
The bomb, packed inside a Jeep, went off as two police officers approached it after residents complained about the suspicious vehicle, said Gen. Jorge Daniel Castro, Bogota's police chief.
The blast killed both policemen and four civilians and wounded 12 other people, Bogota Mayor Antanas Mockus told reporters.
"This is an unacceptable act of terrorism," Mockus said.
Castro said the bomb was apparently placed to cause maximum casualties.
"This is a strategic, busy place with a lot of commercial business, and it appears they (the bombers) strategically selected it to create this impact," the police chief said.
Teodora Lagos, a cleaning woman, was going to her job at a nearby bank when the explosion rocked the neighborhood with a thunderous blast that shattered windows in a one-block area. Many of the shops were still closed and covered with metal shutters, minimizing damage.
"We all ran out and looked around. There was smoke everywhere," Lagos said. "I saw four dead people, including the woman who sells coffee here.
"This violence must stop," she shouted. "Why must innocent people die?"
The attack occurred on a narrow street as employees were arriving for work in San Andresito, which is filled with electronic, clothing and liquor stores. Many of the goods are contraband and cheaper than those found elsewhere.
The vendors are often targeted by violent criminals seeking "protection" money. Police said members of a right-wing paramilitary group have recently been muscling their way into San Andresito and money from its vendors.
Police offered a reward of 50 million Colombian pesos (about US$17,500) for information leading to arrests.
Authorities, however, did not discount that rebels might be responsible for the bloodiest attack in the capital since the El Nogal club was bombed in February.
Leftist rebels fighting in Colombia's 39-year-old civil war have increasingly been bringing the war to the nation's cities. In February, members of the Revolutionary Armed Forces of Colombia, or FARC, bombed an exclusive social club in the capital, killing 36 people and injuring 160 others.
The FARC was also blamed for an attack on a nightclub in the city of Florencia in late September that killed 12 people and injured dozens of others.
Colombia's war pits the rebels against the government and a right-wing paramilitary group. About 3,500 people, mostly civilians, die in the conflict each year.
Three of the militant groups involved in the conflict are on the U.S. list of foreign terrorist organizations: FARC, the ELN or National Liberation Army, a smaller leftist rebel group; and the United Self-Defense Forces/Group of Colombia, a rightist paramilitary organization.
Some of the groups are believed to use the drug trade to fund their war. The U.S. has provided more than $1.7 billion to an initiative known as Plan Colombia that aims to break the link between militants and the drug trade. U.S. soldiers have served as advisers for the Colombian military as part of that plan.