The man, 57, took out a meat cleaver and attacked fellow employees as they travelled on the company bus to work.
Most of the victims went to hospital for treatment but suffered only minor injuries.
The man was subdued by passengers and was later arrested by police. His motive for the attack was not immediately known.
The bus was carrying more than 20 people when the attack happened in Tuen Mun district, about an hour away from Victoria Harbour, local media reported.
"The man suddenly attacked a few of the female colleagues and a male colleague who were sitting on the back rows of the bus a few minutes after it set off," police inspector Kelvin Ip told media.
"We found a cleaver, which we suspect to have been used to attack the people, at the scene," he said, adding there was blood on the knife.
The man had no previous history of mental illness, police say.
One of the female passengers had a finger cut off, according to reports.
The incident follows a number of recent knife attacks in mainland China.
One Monday, police in Shenzhen - an hour's train away from Hong Kong - detained a man for stabbing three people to death.
His arrest came days after another man was arrested in Henan province for a knife attack that killed five.
A man has attacked passengers on a bus in Hong Kong with a knife and injured at least 11 people, reports say.