With just days left until classes resume, British Columbia's fastest-growing school district is still struggling with some major growing pains.

Despite an NDP promise to create enough space, thousands of students in Surrey will find themselves in portable classrooms when they return to school Tuesday.

The district expects about 850 new students this year. That's the equivalent of two full elementary schools, and Surrey has been seeing similar growth over the past several years.

"Of course, those are projections," said school district spokesperson Doug Strachan. "By the time we get to the end of September, we could be looking at more than that."

Schools in the region will be using a combined 333 portable classrooms this year.

In South Surrey, Sunnyside Elementary will start the year with 11 portables thanks to rapid residential development in the area. When Sunnyside first opened in 2013, it was across from a forest that has since been replaced with hundreds of new homes.

"We see a lot of families moving in. It does concern me," said Candice Mah, an expecting mother who's already worried about finding a space for her child.

"Hopefully our kid will have a good school to go to and not be overcrowded."

With Surrey expected to become the most populous city in the province by 2041, there is concern that the new schools that have already been planned might not be enough to keep pace with all the new families moving into the area.

"It's going to take a year or two or three to start to see portables being hauled out," said provincial Education Minister Rob Fleming.

The minister also blamed the 2017 B.C. Supreme Court decision that imposed limits on class sizes for the extent to which school districts are having to rely on portables.

The ruling has also meant that many on-call teachers have had to be moved into full-time positions in order to serve the greater number of individual classes.

"It left the substitute teachers list in short supply," Fleming said. "We've begun to replenish that. We sent letters out to licence-holders who aren't currently teachers. Some of them would be recently retired."

But only time will tell if that list will be long enough by the time cold and flu season hits later this year.

With files from CTV Vancouver's Ben Miljure