More than 40 people have been hospitalised in Las Vegas since Friday, as a heatwave blistered parts of the US.
Las Vegas fire and rescue spokesman Tim Szymanski said: "We will probably start to see a rise in calls Sunday and Monday as the event prolongs.
"People's bodies will be more agitated the longer the event lasts and people may require medical assistance".
More top news
Philip Thomas doesn't like to dwell on the disaster that buried him alive - but he can still recall in detail how an unpaid debt saved him.
The deal would set up a free trade zone between the EU and Canada - and could be an important test for the UK's Brexit negotiations.
A mother has won her battle against the Home Office to allow her Nigerian sister into the country - so she can undergo a marrow transplant.