The Freeport liquefied natural gas (LNG) export terminal in Texas is expected to be offline for at least three weeks after an explosion rocked the facility Wednesday morning, dealing a blow to a global gas market already short on supplies.

State and federal agencies, including the Pipeline and Hazardous Materials Safety Administration, are aiding Freeport LNG Development LP in an investigation to determine what caused the accident. A spokesperson for the U.S. Environmental Protection Agency noted that state and local agencies had not requested its assistance.

The company has taken over incident command, according to state regulators. Freeport spokesperson Heather Browne said the company would not comment on the extent of the damage, where the blast occurred, or how its...