British Columbia's top doctor says she's pleased a travel ban between Canada and the United States has been extended but anyone seeing American licence plates north of the crossing should not be quick to judge.

Dr. Bonnie Henry says some Canadians living in the US may be returning to care for family members and given the sharp rise in COVID-19 cases south of the border it's not surprising they're in BC.

The border closure has been extended by another 30 days for a fourth time, to Aug. 21, but Henry says considerations may need to be made for students who contribute to research programs at universities.

However, she says the safety of British Columbians means anyone who arrives from the United States must isolate themselves for 14 days.

Henry announced 13 more cases of COVID-19 and says a recent increase in cases is due to more people socializing and perhaps flouting the rules by going to restaurants in large groups, for example.

She says businesses that have reopened need to keep going and that means people have to be ``on their best behaviour.''