A late-night house fire in St. Paul killed one person and forced a man and his son to leap to safety from the second floor, authorities said.

Firefighters using a ladder rescued four other members of the family from a second-level window as smoke billowed from the house.

The blaze was reported to the St. Paul Fire Department about 12:20 a.m. Sunday in one unit of a triplex in the 1200 block of Clarence Avenue, said Assistant Fire Chief Michael Gaede.

The first fire engine crew arrived within 3 minutes, saw heavy flames and smoke on the first and second floors of the northernmost of the side-by-side units, and hoisted a ladder to rescue inhabitants.

A man in his 30s had already jumped from the house and was not seriously hurt, the assistant chief added. He then "sorta caught" his 9-year-old son, who also jumped, Gaede said.

"We would never say, 'Don't jump from a window,' " Gaede said. "They jumped when they felt like they had to."

Firefighters helped the mother down a ladder, along with sons ages 8, 3 and 1, the assistant chief said.

After extinguishing the flames, however, fire personnel began searching the house and found a resident on the second floor with major injuries. He was soon declared dead, the assistant chief said. The man was another family member, but his identity has yet to be released.

Neighbors identified the boys' parents as Mary Kong and Por Yang.

"It's just sad," said neighbor Samantha Yang, whose 10-year-old daughter woke her up during the night to watch the commotion outside.

Neighbor Heather Eng said Sunday that the family members were "nice people."

The whole complex had turned out to witness the blaze the night before, Eng said, adding that the community, a few blocks southeast of Lake Phalen, is tight-knit.

Another neighbor said the fire spread quickly and Yang could be heard screaming.

More than three dozen firefighters were at the scene for roughly 2 ½ hours.

On Sunday morning, Xcel Energy investigators in neon yellow vests could be seen surveying the site and completing safety checks on the gas system. A St. Paul fire inspector was also on the scene.

Investigators are trying to determine the cause of the blaze, but Gaede said they had found nothing suspicious.

Staff writer Erin Adler contributed to this report. Paul Walsh • 612-673-4482