New York, New Jersey and Connecticut have sought to introduce quarantine measures on travellers from American states where Covid-19 cases continue to rise.
Visitors from Alabama, Arkansas, Arizona, Florida, North Carolina, South Carolina, Texas and Utah will be asked to go into self-isolation for 14 days New York state governor Andrew Cuomo said.
Some southern and western states have been reporting record numbers of cases, while the outbreak has been declining in the east.
New York was among the hardest hit place in the United States during the original wave, and is keen to avoid a resurgence.
So far, the US has recorded more than 2.3 million cases of the virus and more than 121,000 deaths – the highest number in the world.
The University of Washington predicts 180,000 deaths in the country by October - or 146,000 if 95 per cent of Americans wear masks.
Anyone found breaking the quarantine could face fines of $1,000 (£800) rising to $5,000 for repeated violations, Cuomo said.
He added that states would be added or taken off the quarantine list depending on the number of new cases per 100,00 people or the rate of positive tests.
Lev Radin/SIPA USA/PA Images