First responders in Waterloo, Ont., say there have been multiple injuries and reports of rocks and bottles being thrown at an unsanctioned St. Patrick’s Day street party near Wilfrid Laurier University.

Waterloo Regional Police Service Const. Ashley Deitrich told reporters around 3 p.m. that the injuries at the party centred around Ezra Avenue were mainly related to slips and falls.

Among those injured was a police officer who was transported to hospital. Deitrich said she wasn’t sure how badly he was hurt.

Region of Waterloo Paramedic Service Deputy Chief Kevin Patendra said that paramedics had received 41 calls and transported 18 people to hospital, mostly for alcohol and drug misuse, and slips, fractures and head injuries.

Const. Deitrich also said that police were looking into reports of property damage and handing out tickets for underage drinking and public intoxication.

“We have been very disappointed with some of the behaviours that have been displayed by some of the people in attendance,” she said.

Deitrich said the crowd appeard to be similar in size or potentially larger than last St. Patrick’s Day’s, when an estimated 22,000 revelers filled the streets.

Earlier, Waterloo Police Chief Bryan Larkin told CTV Kitchener that police were preparing for 30,000 people. He said they had brought in backup from nearby Peel Region and have “a plan in place that will target out-of-towners.” Police won’t hesitate to lay charges, he said.

In London, Ont., police told CTV London that they had responded to several house parties in the early afternoon and one of them was shut down by fire officials.

London Police Service said on Twitter that a male had been transported to hospital with unknown injuries after falling from a residence’s roof.

London has experienced riots on St. Patrick’s Day in the past. In 2012, a crowd of roughly 1,000 people started fires and threw bricks and bottles at emergency responders near Fanshawe College.

There was also a heavy police presence on Sunday in the nation’s capital, but police told CTV Ottawa early on Sunday afternoon that there had not yet been any reports of vandalism or overdoses.