City workers, partner organizations and volunteers are finishing preparations at the Kay Bailey Hutchison Convention Center in downtown Dallas for evacuees from Hurricane Harvey.
As many as 5,000 evacuees may begin arriving some time Tuesday.
Earlier Monday, Dallas Mayor Mike Rawlings said the "mega shelter" would optimistically be ready late Monday.
City officials began preparing the lower-level air-conditioned garage as a shelter on Sunday. The city is currently operating three additional shelters at recreation centers that are near capacity.
Rawlings said Monday afternoon more than 500 people from Galveston would be flown to North Texas.
"Today we are going to start receiving ... individuals that are going to be flown out of the Galveston area. The state has eight, nine different planes and we will be receiving at Love Field, 50 to 80 people on each of those flights," Rawlings said. "There will be individuals, their animals as well, and we will start to triage those individuals and figure out where we can put them."
The Dallas mega shelter will include a medical facility that will be able to perform basic medical care, however those needing additional care will be sent to area hospitals.
The city of Houston has 250 buses on standby ready to move evacuees from the city. When they arrive will be determined by road conditions exiting the city; Rawlings said it could be another 48 hours before Interstate 45 is available.
"If Houston is not able to take care of all of those citizens' needs, they'll start moving them north and that's when we'll start receiving," Rawlings said.
Rawlings said city officials are preparing for the possibility that the mega shelter may, too, reach capacity.
"We may have thousands, upon thousands, upon thousands or more individuals that will even get bigger than this convention center. I'm not saying it's going to happen, but we've been asked to prepare for numbers that could be up in the tens of thousands. To that end, we are looking at other areas in the city of Dallas."