A youth died as he attempted to flee from youths who had stabbed him while posting posters of a Starehe MP aspirant.
The man was killed by a speeding car at Pangani, Nairobi while another person he was with was injured during the fracas.
Nairobi county commander Japheth Koome said the two were accosted by a group of youths allied to the politicians' competitor.
Koome, who did not give the names of the aspirants that the two groups are allied to, said the two groups clashed at around 6am.
"The attackers spotted the two young men who were putting up campaigns posters."
"A confrontation ensued where the two were stabbed," Koome said on Wednesday as Jubilee primaries kicked off in Nairobi.
"Unfortunately, the youth who was hit by a vehicle as he attempted to flee from their attackers died."
"The other one is still in the hospital. A postmortem will be conducted to establish what killed the young man," he said.
The Nairobi police boss condemned the attack adding that it was illegal for the aspirants to put up posters when polls were being conducted.
Police have been deployed in various polling centres in the city to avert chaotic incidents during the hotly contested primaries.
Senator Mike Sonko, Former Starehe MP Margaret Wanjiru will face it off with former Gatanga MP Peter Kenneth for the JP ticket.
The three are eying the ticket so as to compete with ODM's Evans Kidero during the August 8 polls.
GSU officers were deployed in marked hotspots including Starehe, Dagorreti South, Kamukunji, Kasarani, Roysambu, Embakasi East, Embakasi West and Embakasi Central.
Ballot papers were escorted under security to the centres ahead of the start of the exercise.