A 16-year-old boy was among those killed
"Three of their accomplices managed to escape,” a security source said.
Mombasa county police commander Johnston Ipara said the suspects were armed with machetes and knives.
Police in the county have been on the spot over the killing of suspected criminals.
Police killed three suspected gangsters in Utange, Mombasa, on Thursdays night.
The three were gunned down near Utange Primary School in Bamburi while three others managed to escape.
The Nation established that a 16-year-old boy was among those killed.
"Three of their accomplices managed to escape as they were being pursued by the officers. They were all armed with machetes," said a security source.
A community policing official Godffrey Masamba said those killed are suspected to be members of a criminal gang in Kisauni.
"These youth have been responsible for the many robberies in the area," Mr Masamba said, adding that the bodies had been moved to the Coast Provincial General Hospital (CPGH).
Mombasa county police commander Johnston Ipara confirmed the incident, saying the suspects were armed with machetes and knives.
"We recovered the weapons from the suspects who were attacking people within the area," Mr Ipara said.
The killings come a week after two suspected robbers were shot dead by police in Mwandoni in Kisauni sub-county.
Police in the county have been on the spot over the killing of suspected criminals, with allegations that officers have been shooting innocent people during their operations.
On Tuesday, police shot Mr Issa Baya twice during a robbery at his neighbour's house in Kisauni constituency. He worked as a caretaker.
Two weeks ago, an eight-year-old girl was also hit by a stray bullet when police were reportedly pursuing suspected criminals.
The girl was discharged last week from CPGH after a bullet lodged in her thigh was removed.