Wildfires have forced more than 3,500 residents of Kelowna to leave their homes for the second time in less than two weeks.

Two more evacuation alerts have also been issued for areas near the fire. The new alerts affect about 9,600 people in southeast Kelowna and brings the number on evacuation alert to more than 15,000.

Hot, dry weather and winds are fanning new life into the Okanagan Mountain fire and firefighters are struggling to keep the flames from jumping firebreaks.

View from South Kelowna

Officials say only a heavy rain will allow them to put out the 21,000-hectare fire, but no rain is forecast until at least Sunday.

B.C. has been suffering its worst forest fire season in decades, with more than 2,300 fires recorded since late spring.

On Thursday, the fires claimed five historic railway trestle bridges near Kelowna, and the chances of saving the remaining 11 bridges are slim.

Most of the trestle bridges are part of the Kettle Valley Railway trail. They are made of wood soaked in creosote and date back 100 years.

The bridges were restored recently to become part of the Trans-Canada Trail and are popular with hikers and cyclists from all over the world.

"I'm very much afraid given the forecast today, and what's been happening, that likely most of the structures in Myra Canyon will be lost today," said fire commander Brian Kempf.

The trestles were designated a national historic site in January and volunteers had painstakingly restored and repaired the wooden, creosote ties, turning the trestles into a lucrative tourist attraction.

The terrain around the testles is rugged and steep, making both fighting the fires and the possible rebuilding of the testles difficult.

It's estimated it could cost more than $30 million to rebuild the trestles.

The Okanagan Park fire continues to burn less than three kilometres from major subdivisions. Kelowna has already lost 250 homes to this fire and after a one-week lull, once again, the city is on high alert.