A massive fire erupted at a Sacramento apartment building under construction overnight into Tuesday. Sacramento Fire says one of their engines was heading back from a medical aid call when they noticed some smoke near 19th and X streets. After investigating it a little further, they encountered the building being engulfed in flames. The building involved is a new, five-story apartment structure that was under construction. An active firefight is still underway as of 5 a.m. Tuesday. A number of streets in the immediate area are closed. Neighbors next to the building were worried for a time that a tree that caught fire would spread to their home. Several cars parked near the building also saw their headlights melted with the heat.