Ottawa police say one youth is dead and the search continues for a second after they fell through the ice on the Rideau River in Ottawa's south end.

Emergency crews responded to a call at 11:44 p.m. Wednesday for four youth who had fallen through the ice along Nicolls Island Road near Manotick.

Police say two youths were rescued by first responders and transported to hospital. A 15-year-old girl and a 17-year-old boy were treated for mild hypothermia, according to paramedics. "Two more youths,16-year-old and 17-year-old males were still missing and believed to be in the water," Ottawa police said in a statement Thursday morning.

"A rescue operation including a surface and water search in very difficult conditions continued through the night."

Police say officers with the Marine Unit and the Ottawa Fire Water Rescue Unit searched the area overnight. The body of one of the missing youths was recovered, police said. The search continued Thursday morning for the second missing youth. "This tragic incident affects us all and we have offered supports to the loved ones of the youths," police said.

An Ottawa police officer was transported to hospital with a dive-related injury, according to paramedics. Ottawa has seen warmer-than-normal temperatures through December, with five straight days of temperatures above 0 C. The temperature hit 6.6 C on Tuesday and 4.1 C on Wednesday.