The Hawaii Department of Education has yet to fill hundreds of teaching positions across the state as school has started for more than 180,000 students.

Officials with the department said there were 625 positions that still needed to be filled as of last week, even after 100 new teachers were hired during the summer. State data show the number of teacher vacancies more than doubled within two months this summer.

In response to the shortage, the department increased its recruitment efforts by sending teams to meet with potential applicants in mainland cities between March and July, including Chicago, Portland, Las Vegas and Los Angeles.

Teacher advocates maintain the department has struggled with hiring qualified teachers because of low salaries.

“More teachers are leaving, and fewer teachers are going into the profession,” said Corey Rosenlee, president of the Hawaii State Teachers Association, which represents 13,500 teachers. “We cannot find even emergency hires for these positions.”

The labor contract for teachers expires next summer, and Rosenlee told the Honolulu Star-Advertiser that the union plans to advocate for better working conditions.

“If we want to fix the teacher crisis in Hawaii, we have to empower teachers, treat them like professionals and pay them like the professionals they are,” Rosenlee said.

DOE officials contend that the hiring process is selective and that more focus on a mentoring program for new teachers will continue to boost retention rates.

“Our overall trend is positive with regard to our retention of teachers in their first five years,” said Stephen Schatz, deputy superintendent for the Department of Education. “We have reason for optimism.”

Data from the 2014-15 school year, the latest state figures available, show that of the 785 teachers hired in school year 2010-11, 60 percent were still employed five years later, marking the highest five-year retention rate in at least a decade.