Local police chief Japheth Mwania said that six of the dead were gunmen suspected of being members of a 100-strong group that attacked Ukunda on Thursday. The two others were civilian bystanders caught in crossfire, he said.
Mwania, recently assigned to Mombasa to deal with the violence there, said a one-year-old child was missing after its mother was attacked on Thursday night.
One person died and two were wounded, and witnesses said the attackers razed 100 kiosks and 70 buildings.
Mwania said police had recovered two stolen police firearms.
Last Friday up to five people, including a two-year-old child, were hacked to death and 20 seriously wounded by heavily armed raiders in Mombasa's Likoni suburb.
Areas around Mombasa have suffered a wave of violence since August in which more than 40 people have been killed.
Tens of thousands of people have fled since President Daniel arap Moi, 73, ordered a police crackdown on violence.
Moi, who has been in power for 19 years, accuses the opposition of fuelling tribal tensions before a general election this year. But many "upcountry" people leaving the coast say the government wants them out because they would vote for the opposition.
On Thursday, Kenya's parliament formally adopted constitutional reforms intended to avoid bloodshed ahead of the elections.
They provide for the repeal of laws which allow detention without trial and approve the expansion of Kenya's electoral commission to bring in members nominated by the opposition.Reuse content