The US–Canada border has closed to nonessential traffic, President Trump announced on Wednesday morning, bringing ongoing novel coronavirus containment efforts to a new level.

“We will be, by mutual consent, temporarily closing our Northern Border with Canada to non-essential traffic,” the president tweeted. “Trade will not be affected. Details to follow!”

According to The Washington Post, the Department of Homeland Security is still working out the specifics of the closure, but it’s likely to make an announcement in the coming days. The policy would not apply to commercial goods or citizens and legal residents of the United States. It’s unclear how long the closure will remain in place.

The Wall Street Journal reported on Tuesday night that the Trump administration was considering some kind of comprehensive border closure, including new restrictions on migrants and asylum seekers on the US border with Mexico. Trump has placed similar restrictions on visitors from China, Europe, and the UK.

Public health officials have been broadly skeptical of the effectiveness of travel restrictions in containing the ongoing outbreak in the US. With more than 6,500 confirmed COVID-19 cases, the disease caused by the novel coronavirus, in the US (and likely tens of thousands more still undetected), most experts see community transmission as a greater danger than transmission from foreign travelers. Nevertheless, those restrictions have been a centerpiece of Trump’s strategy, beginning with the China travel ban announced in January.