In the US, the death toll from Covid-19 has now passed 100, as the coronavirus reaches all 50 states.
The US and Canada have jointly agreed to close their land border to non-essential traffic, but trade will not be affected.
Nearly 8 million people in northern California are being asked to stay at home and the mayor of New York says a similar measure is being considered there.
Many schools may remain closed for the rest of the school year - until the end of August.
Washington correspondent Giles Gibson speaks to Corin Dann.
