In the most drastic move yet to try to slow the spread of the novel coronavirus, Gov. Jay Inslee is expected Wednesday to restrict gatherings of more than 250 people in King, Snohomish and Pierce counties, a move aimed at sports, concerts and other cultural events.

The measure will be announced during a Seattle news conference, according to a source involved in conversations with the governor’s office but who has not been cleared to discuss the issue. The measure would not affect retail stores, according to the source.

The restriction applies to large public gatherings such as baseball games, concerts and cultural events, another source told The Times.

Chris Reykdal, Washington’s superintendent of public instruction, said Tuesday evening he doesn’t expect Inslee’s announcement to shut down public schools.