A man in his mid-30s who went into cardiac arrest near the Pretoria Bridge while running in an Ottawa Race Weekend event on Sunday died later that day, according to Ottawa police.

The runner was taken to hospital in life-threatening condition, paramedics said on Sunday.

Both the half and full marathons took place Sunday morning. An Ottawa Race Weekend spokesperson said organizers didn't know who the man was or which race he was participating in when he collapsed.

He has not been identified.

"We are deeply saddened to hear of the passing of one of the participants in this weekend's events," John Halvorsen, the organization's outgoing race director, was quoted saying in an emailed statement Monday.

"Our thoughts and prayers are with his family and friends. Thank you to the first responders and onsite Ottawa Hospital team, many of whom are volunteers, for their work and support during our event."

Nine other people were taken to hospital Sunday, with one other runner taken to hospital in critical but non-life-threatening condition.

On Monday, several bouquets of flowers were placed at the base of a tree near the spot where the man who died collapsed.

More than 32,000 people took part in the weekend's races.