An early morning house fire killed two young children Tuesday, fire officials said.

The two-story house was engulfed in flames when firefighters arrived just after 6:30 a.m., said Fire Chief Steve O'Connor.

A 1-year-old and a 3-year-old, who were in an upstairs bedroom, died in the blaze, O'Connor said.

Two adults jumped out of a second-story window and were taken to a hospital, where they were being treated, O'Connor said. He did not know the extent of their injuries.

"When we got on scene, the floors had already burned through and the front stairs had already burned away," O'Connor said. "A very significant amount of damage had already occurred before we arrived. We just couldn't get to the second floor."

He said the inability of firefighters to get upstairs didn't make a difference in efforts to save the children.

The names of the adults and children were not immediately released.

The cause of the fire was under investigation. Ottumwa is about 85 miles southeast of Des Moines.