Two men are behind bars after two separate attacks on Winnipeg Transit buses Wednesday, and police are concerned about the level of violence in the cases.

"Both of these are occurring during the midday; they're both violent incidents with the potential to have more than one victim," said police spokesperson Const. Tammy Skrabek.

The first attack, which police characterized as random, happened just before noon on Wednesday.

A 24-year-old man boarded a bus at the University of Manitoba campus through the back door without paying his fare, police said.

A transit inspector got on the bus shortly after and tried to speak with him. The man spit on the inspector, punched him and ripped his uniform.

The bus driver and inspector held the suspect until police arrived, Skrabek said. He is charged with assault, uttering threats and mischief.

Less than two hours later, police were called out after a violent incident was reported on a bus near Tuxedo Avenue and Corydon Avenue.

A 43-year-old man choked a 45-year-old man to the point of unconsciousness in an unprovoked act, police said. When a second man on the bus tried to help, he was also choked and beaten.

The two passengers had minor injuries and were treated by paramedics. They did not need to go to hospital.

The accused faces assault charges.

He is is known to police and drugs may have been a factor, Skrabek said.

Transit driver Irvine Fraser, 58, died after being attacked at the last stop on his shift in February. (Facebook) Police are seeing more of these incidents, and passengers need to watch out for odd behaviour, she said.

"All you can do as a passenger is just sort of be aware. I know when I'm sitting on the bus, a lot of people have their heads down in their cellphones and headphones on. You know it's important to take a look at who's coming on and off the bus."

Transit workers have been on edge after a series of attacks on bus drivers in recent months, including the killing of Irvine Fraser, 58, earlier this year.

Transit union wants more training, security

Amalgamated Transit Union president Aleem Chaudhary said the driver in the first incident followed protocol "all the way," but he wants to see more training for operators and supervisors on Winnipeg buses.

Currently, drivers receive less than half a day of training on how to protect themselves from assault, he said, as part of a roughly four-week general training program when they're hired.

"As a union, we want to take a further step to increase the security on buses so people can feel safe, and these kind of incidents are less and less, and hopefully never," he said.

The city has promised the union five new security personnel, he said; he hopes that takes the form of a special transit police service.

"We're hoping to get our own transit police who can react faster and be trained to handle this situation. When you get properly trained people, they can assess the situation right away and react to it properly," he said.

Chaudhary called the environment on buses generally safe but "unpredictable."