Port Alberni RCMP arrested a suspect after an officer and firefighters spotted a woman adding material to a downtown blaze.
It was one of three fires crews responded to in less than a day.
The woman was arrested Tuesday after emergency crews responded to a fire at 3rd Avenue and Harbour Road about 8:35 a.m.
The woman ran off but was arrested a short distance away.
A second investigation is underway into a suspicious fire in an attached shed at a residence on 2nd Avenue about 2:45 p.m. Monday. The fire was quickly controlled.
Police are also looking into a vehicle fire about 11:55 p.m. Monday on 4th Avenue.
The Port Alberni Fire Department kept the flames from damaging any surrounding property.
Police are seeking witnesses and video surveillance footage from nearby businesses and residences in each of the incidents.
They asked people to be cautious outdoors given hot, dry conditions in the Port Alberni area.
The forecast called for a 40 per cent chance of showers in Port Alberni on Wednesday, followed by six days without precipitation.
