"The crowd is unruly and we want to disperse them, that is why we're using helicopters," a police commander told the AFP news agency.
The incident came as Kenya's opposition leader said that the country was "drifting into a state of anarchy".
A Kenyan opposition politician was shot dead outside his home in the capital, Nairobi, early on Tuesday.
Police said that they were not ruling out "political motives" connected to the disputed presidential elections on December 27 in the killing of Mugabe Were, an Orange Democratic Movement (ODM) politician.
"We suspect a foul hand of our adversaries in this," Raila Odinga, the ODM leader, said.
"Of course there are lots of rumours going around. We hope and expect that investigations are going to be carried out by the law enforcement agencies, but as you can see, the country is drifting into a state of anarchy."
Police said that two men shot Were as the politician drove up to the gates of his home in the Woodley district just after midnight, then fled the scene.
"We have launched investigations," Julius Ndegwa, the Nairobi area police chief, said.
"The two criminals who shot him did not steal the car or anything else."
Police fired tear gas at mourners who had gathered at Were's home, allegedly taunting officers. Outside dozens of protesters manned burning barricades of tires and uprooted telephone posts.
Al Jazeera's Yvonne Ndege, in Nairobi, said that the police had told her that they are not treating this as a political murder. Instead they say one of the city's frequent violent crimes, such as a car jacking, may have led to the death.
Yet Ndege said there's "every possibility" that Were was killed by a rival candidate for the seat in the December 27 legislative vote, held at the same time as presidential elections. The seat is now vacant after Were's death.
"As a consequence of this there has been some fighting taking place in Kibera - one of the biggest slums in Africa and an opposition stronghold - where people on the ground have reported seeing at least two bodies," she said.
"In Mr Were's constituency, called Embakasi, there is a lot of tension. Apparently rowdy youths have been gathering in the market and several kiosks have been burned."
The Reuters news agency witness reported that he saw seven corpses in the Nairobi slum, some with cuts on their heads and necks.
Naivasha has seen some of Kenya's worst violence in recent days after largely avoiding the unrest in the first few weeks that followed the disputed re-election of Mwai Kibaki, the president.
Many from the region's Luo and Luhya communities have fled from gangs of ethnic Kikuyu, Kibaki's tribe, who had vowed revenge for the killings of members of their community in other parts of the country.
"I am not at all happy to stay around here. We are big enemies now," Samson Matovo, a Luhya who had taken refuge at the police station, said.
"Even if it calms down over the next few weeks, it will erupt again."
Crowds set fire to homes and thousands of looters smashed shop windows in the town before the helicopter attack on Tuesday.
Five police officers fired into the air but were unable to control the mob of about 5,000 people. Naivasha's police chief tried to calm the crowd, but was pelted with stones and fled in his car.
Outside the police station, David Chege, a Kikuyu businessman, said: "They are the ones who started all this. They should all leave."
Amid the chaos, mediators led by Kofi Annan, the former UN secretary general, said they would launch formal dialogue between Kibaki and Odinga.
However, Odinga has repeated his call for Kibaki to agree "that this election was stolen".