Washington DC - A dangerous heat wave is expected to sweep across much of the central and eastern US beginning Tuesday and lasting through the July 4th weekend, when the country celebrates its 250th birthday and hosts knockout stages of the World Cup.

Temperatures are forecast to soar above 100F, with high humidity pushing heat indexes even higher, the National Weather Service warned Monday.

Overnight cooling will be limited, with many areas seeing lows in the mid- to upper-70s, the agency added.

That combination of prolonged daytime heat and little nighttime relief is expected to increase the risk of heat-related illness, particularly for the most vulnerable.

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"Drink water often. Limit time outside in the afternoon. Check on neighbors," said the public alert system in the nation's capital.

The heat wave arrives as the US prepares to mark the 250th anniversary of its independence from Britain, with Washington DC set to host what organizers say will be the largest fireworks display in history.

The World Cup has meanwhile entered its knockout stages, with several matches set to take place in the sweltering conditions.

More frequent, longer-lasting, and more intense heat waves are one of the clearest signs of climate change globally, with Europe also recently hard hit.