JANESVILLE, Wis. -

Officials said the careless discarding of smoking materials was the cause of an apartment fire in Janesville Thursday that caused more than $12,000 in damage.

The Janesville Fire Department was dispatched to the 1400 block of Canyon Drive around 12:15 p.m. for reports of a possible structure fire, according to a release.

The fire was reported by tenants in an adjacent apartment complex who had noticed smoke coming from a first-floor bedroom window, officials said. Firefighters discovered the fire started in the apartment’s bathroom.

The fire was confined to the bathroom and extinguished, according to the release. Smoke and heat damage contributed to an overall estimated loss of $12,500 to the property and contents inside.

Tenants of the apartment building evacuated after an alarm system went off, officials said. No one was home at the apartment where the fire started.

In an interview with a tenant later, investigators determined an ashtray had been emptied into a bathroom trash bin earlier in the day.