WASHINGTON, United States (AFP) — Blistering temperatures and humidity gripped swaths of the United States (US) on Wednesday, with the worst yet to come for the densely populated East Coast as the nation co-hosts the World Cup and prepares to celebrate its 250th birthday.

“Heat dome” conditions — in which high-pressure systems trap warm air like the lid on a pot — persisted over the Midwest and South and were moving east, with some 46 million people under heat alerts.

“We are entering what could be the most extreme heat wave this city has seen in over a decade,” New York Mayor Zohran Mamdani said in a video, adding he wanted people to stay safe while watching the World Cup, celebrating the Fourth of July or — he joked — “renting out MSG to get married, hypothetically.”