A manhunt was underway for the unidentified person reported to have deposited the luggage in a cart, Ndolo said. Detectives think the luggage contained an improvised explosive device that went off, a police officer at the scene told The Associated Press.
The officer spoke on the condition of anonymity because he was not authorized to speak to reporters. The Kenya Red Cross said it sent emergency teams to the scene, which was sealed off by law enforcement officers.
The explosion happened two days after the U.S. Embassy in Nairobi issued a security alert reminding the public about "the continued need for sustained vigilance in public spaces such as shopping malls, hotels, and places of worship."
Kenya is recovering from a Jan. 15 attack in which gunmen stormed a hotel complex and killed 21 people. The Islamic extremist group al-Shabab, which is based in neighboring Somalia, claimed responsibility for the attack on the DusitD2 hotel and shopping complex.
Al-Shabab, which has ties with al-Qaida, has often targeted Kenya in retaliation over Kenya's military involvement in Somalia. Al-Shabab also carried out the 2013 attack at Nairobi's nearby Westgate Mall that killed 67 people, and an assault on Kenya's Garissa University in 2015 that claimed 147 lives, mostly students.