Two blasts struck the Somali district of the Kenyan capital on Tuesday, leaving at least one person wounded, the Red Cross said on its Twitter feed.
"One casualty has been evacuated," the Red Cross said.
The blasts came as results were trickling in from Kenya's presidential polls, although the predominantly Somali district of Eastleigh has in recent months been the target of several attacks attributed to sympathisers of Somalia's Shebab insurgents.
Nairobi police chief Benson Kibui confirmed only one explosion, saying it happened when a homemade explosive device was thrown at a kiosk, wounding a woman who was inside.
"She sustained injuries and was rushed to hospital," he told AFP.
"The device landed near a bar where people had been watching the election results on television," he said, adding police did not know what the bomber was targeting.
The explosion occurred near a mosque where a Kenyan MP was wounded in a grenade blast late last year.
Eastleigh, often referred to as Little Mogadishu because of its large Somali population, has been the target of small-scale attacks since Kenya sent forces into Somalia to fight the Shebab in late 2011.
The Coast region and the towns along Kenya's border with Somalia have also been hard hit.