US President Joe Biden has announced measures to try to tackle the effects of extreme heat as 46 million Americans suffer under heat advisories.

Major cities including Boston, Philadelphia, and Washington, DC, were under heat emergencies on Thursday.

The actors' union Sag-Aftra, which is on strike, was forced to pause picket lines amid New York City's excessive heat warning.

The extreme heat is expected to last through the weekend.

"I don't think anybody can deny the impact of climate change anymore," President Biden said on Thursday at a White House press conference.

He said heat is the "number one weather-related killer" in the US, causing 600 deaths each year.

Mr Biden unveiled new measures designed to help workers most vulnerable to heat, increase funding for weather forecasting, and expand water storage capacity in the western states and make buildings more heat-resistant.

"The construction workers who literally risked their lives working all day in blazing heat, and in some places don't even have a right to take a water break, that's outrageous," he said.

Earlier this week, Texas Congressman Greg Casar held a food and water strike to protest against a Texas law overriding protection for people working outdoors in intense heat.

He cited the death of a 40-year-old postal worker who died on his route, and a 35-year-old believed to have died of heat exhaustion while working to restore power in Texas' Harrison County.

Sweltering humidity is exacerbating the high temperatures in some parts of the US, increasing the heat index - which means, what the temperature feels like to humans when humidity is combined with the air temperature.

In Washington, DC, and New York City, temperatures are expected to feel like 107F (41C) and 105F (40C) respectively, on Friday.

East coast night-time lows between now and the weekend will be as much as 10 to 15 degrees Fahrenheit above average for the region, according to the National Weather Service (NWS).

And record-breaking heat continues to bake the Southwest and Central US.

Phoenix, Arizona, has now endured 28 consecutive days with the mercury at or above 100F (38C).

The evenings have offered little respite - overnight temperatures have not dropped below 90F (32C) for at least 16 days.

El Paso, Texas, has surpassed even Phoenix, hitting 40 consecutive days of temperatures at or above 100F (38C) on Tuesday.

In addition to the scorching weather, some parts of the US are facing intense thunderstorm systems.

Some 180,000 people are without power in Michigan after a storm soaked the region and downed power lines on Wednesday.

The Upper Midwest and Great Lakes are forecast to get more thunderstorms, which could bring 75-mph winds and golf-ball-sized hail, on Thursday afternoon into Friday.

Those storms will then spread into the Northeast and Mid-Atlantic late Friday into Saturday, the NWS predicts - bringing damaging winds, hail and possible flash flooding. (BBC)

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