TORONTO — Ontario's four major teachers' unions say they want the government to establish specific benchmarks that would trigger moves to in-person or virtual learning.

They say that needs to be part of a provincial plan for the safe return of students to in-person classes during the pandemic.

All students are currently learning online and the government announced on Thursday that schools in southern Ontario will remain closed for in-person classes until Jan. 25.

The province cited surging rates of COVID-19 for the decision and said it planned to bring in new measures to make schools safer.

The unions say in a joint statement that the government should use the closure to take action that includes improved ventilation and enhanced sanitation in schools.

They are also calling for smaller class sizes.