The Calgary Fire Department says a four-alarm fire at an Inglewood condo that forced more than 200 people from their homes in May was caused by a careless smoker.

Officials spoke to witnesses who saw flames emerging from a container between a window and door on a patio. That led them to determine the fire was caused by the careless disposal of a cigarette in a planter, acting fire investigation co-ordinator Travis Thiessen said in a release Wednesday.

The cigarette was likely disposed of around 10:30 p.m. on May 30, where it smoldered for some time before bursting into flame.

Crews arrived on the scene around 1:30 a.m. the following morning. All 64 units of the building were evacuated and 25 fire apparatuses were required to contain and extinguish the blaze, the department said.

"We commend residents for alerting each other as it was a narrow escape for some of them," said Thiessen.

"However, we need to remind all Calgarians to never dispose of smoking materials in planters or plastic containers, and to use caution when using outdoor open flames, including barbecues and backyard fire pits."

1 in 3 recent fires caused by careless smokers

Thiessen said the blaze was part of a recent trend of preventable fires that have been caused by careless cigarette disposal.

"We've seen three careless disposal fires in the last five days," Thiessen said.

"This has been an unusual and extreme year for smoking-related fires in Calgary."

Of 53 building fires in May and June, the department said 17 were related to smoking. Out of the 25 most serious fires, 13 were suspected to be or caused by careless cigarette disposal.

The Calgary Fire Department is warning the public about the dangers of disposing cigarette butts and other smoking material in planters, lawns and gardens. (Calgary Fire Department)

"Residents who accidently start fires in an outdoor flower pot often report they thought it was just dirt. It's not. These are flammable materials that can smolder for hours then ignite the rest of your deck and house," Thiessen said.

The trend may have contributed to an overall increase in fires in Calgary, as May was the busiest month in five years for building and structure fires. The total cost in property loss is estimated at $10.9 million so far for the month, with that number expected to increase as other investigations wrap up.

Careless cigarette disposal accounts for roughly half of all outdoor fires where the fire's cause could be pinned down, the fire department said.

The department shared a few tips for fire prevention: