NFL Commissioner Roger Goodell has instructed clubs to close all team facilities, stepping up league efforts to combat the spread of new coronavirus.

According to a memo sent to all league clubs and reported on NFL.com, the shutdowns will continue to at least April 8.

Goodell told the teams the rules are meant to "ensure that all clubs operate on a level playing field, and that the NFL continues to conduct itself in a responsible way at this time."

All NFL clubs had already suspended normal business operations and barred players from team facilities unless they were there to receive medical treatment.

Most if not all clubs had a limited number of staff working in their offices even as health authorities around the United States recommended people stay at home in a bid to slow the spread of the virus.

Now Goodell has told clubs that from Wednesday night the only personnel allowed at team facilities will be those providing ongoing medical treatment to players, and those required to maintain the security and operational capabilities of the facilities.