The injured were taken to nearby hospitals and the Kenyan Red Cross was setting up a blood donation center, the center said on its official Twitter feed.
"Two explosions reported. First blast was from a 14-seater matatu (minibus), second blast within Gikomba Market. Four fatalities," NDOC said on its official Twitter handle.
Kenya has been rocked by a series of blasts since September's deadly attack on a luxury shopping mall by Somali militants. It was not immediately clear who carried out Friday's attack.