Transit officials are still unsure why a Winnipeg Transit bus with passengers aboard filled with smoke and then burst into flames.

It happened Saturday afternoon on Portage Avenue.

“The bus makes it over to the side of the road,” said witness Brad Mastervick, “Next thing you know, within a minute or two of her stopping there was flames pouring out of the back end of the bus.”

The blaze is concerning to some transit users.

“That’s why I sit at the front,” said Mike Shea, “To get out fast, you know.”

Saturday’s incident is just the latest in a string of bus fires over the past several years.

In 2011, a bus caught fire on Sherbrook Street and two years before that another bus burned on Pembina Highway.