SEE: Nearly 200 Firefighters Battling Massive Houston Blaze Resulting From Explosion

A massive fire at a Houston gun warehouse sent a huge fireball into the sky and prompted Houston officials to issue a shelter-in-place because hazardous materials had been sent into the sky.

Late Thursday, emergency officials lifted the shelter-in-place suggestion but the fire persists. Irving firefighters tweeted a picture from the scene illustrating the stubborn nature of the conflagration they and some 170 other firefighters were furiously trying to extinguish.

City officials still are telling residents near the fire to turn off their air conditioners, close their windows and take shelter in a central room in their homes or offices.

Students from a nearby elementary school have been evacuated to an area high school and are being picked up by their parents. Fox 26 in Houston station reports up to 600 schoolchildren have been evacuated, moved to safer ground at the Don Coleman coliseum.

Parents were being asked to bring proper identification as they picked up their children at the coliseum.

The scene is utter chaos, even firefighters unsure how many buildings have been engulfed by the flames: "170 firefighters battling four alarm fire in Spring Branch, Fox 26 quotes a firefighter as saying. "Hard to know how many buildings affected."

The 4-alarm fire began just before 10 a.m., according to NBC News, starting as a housefire in a nearby neighborhood before engulfing A-1 Custom Packaging.

The warehouse contains guns and ammunition that could ignite or explode, and 175 firefighters are on the scene, NBC News reported.

The massive blaze has prompted cancellations and re-scheduled events throughout the region. Newspring Art Studio, a non-profit catering to at-risk youth, has cancelled all of its after-school activities as a result of the fire, according to a tweeted post officials sent out.

Residents are urged to continue monitoring local media for updates and also at houstontx.gov/emergency and official social media outlets for updated information. The City of Houston emergency notification system is continually sending updates via its Internet portal.

This is a developing story and will be updated.

See scenes from the fire below:

Main image: NBCNews screenshot

>>> Tony Cantu contributed to this report.