Gunmen killed seven people among them four police officers on Friday evening at Mambo Sasa forest in Witu division,Lamu county.
Among those killed was a Tahmeed bus driver,a Toyota Probox driver and a passenger.
Daniel Kahosho, head of Kenya Police Reservists in Mpeketoni in Lamu County, told Reuters the gunmen blocked the bus with their car and then sprayed it with bullets.
"Two lorries which were carrying mangoes were also attacked," he said.
"We still don't know how many of the passengers may have been hijacked. The bus is riddled with bullets."
The bus conductor and eight passengers were injured during the shootout and are receiving treatment at Mpeketoni Sub County hospital
Kache Kombe,one of the passenger, told journalists at the Malindi sub county hospital that the gang fired indiscriminately at the bus forcing the passengers to hide under seats.
Kombe said her husband was shot on the chest while shielding her.She carried her injured husband for over 10 kilometres before he died due to excessive bleeding.
Lamu county commissioner Miiri Njenga said the attack took place at around 6.30pm at Kona Mbaya area near Mambo Sasa forest in Witu. The bus had left Malindi town at 4pm.
Njenga said the attackers blocked the road with a Toyota Probox they had carjacked forcing the bus driver to stop.
"A border patrol vehicle that was manning the area managed to spot the bus and arrived at the scene. That is when a fierce gun battle that lasted several minutes ensued, during which five people died and several were injured," said Njenga.
The attackers are said to have fled back into Mambo Sasa forest. No arrests have been made.
Following the incident security has been beefed up in Witu and the entire Lamu county which has seen more than 100 people killed in the last two months.