Thousands of Americans were stuck in large crowds in US airports for hours after President Donald Trump announced a ban on travel from many European countries and the US.

Photos showed people standing shoulder to shoulder, while others had to wait for up to seven hours to be screened.

Travellers said people with symptoms or diagnoses were not properly separated, workers did not appear to have protective gear, people in the queue were sharing objects, and healthcare workers used incorrect terms such as "China flu."

Health experts and state politicians have criticized the crowding and said it could help the virus spread.

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Thousands of Americans flooded US airports over the weekend after President Donald Trump abruptly announced a ban on travel from European countries in a bid to stop the spread of the coronavirus.

The ban — which came into effect on Friday night for 26 European countries, and will do so for the UK and Ireland on Monday at midnight — does not stop US citizens and some other groups from entering the country from Europe.

As an increasing number of European countries went into lockdown, and airlines issued warnings of reduced flights, many Americans rushed to fly home, in some cases paying up to $20,000 to travel.

But once they reached the US, they faced long lines and densely packed crowed as they waited for hours to go through customs and get health screenings.

This was among the many public-health issues on display as health authorities advise people to stay far apart to stop the spread of the virus that has now killed over 6,500 people and infected more than 169,000 worldwide.

Jeremy Konyndyk, a senior policy fellow at the Center for Global Development, tweeted in response: "Good God. You could hardly invent a better scenario for superspreading events."