At least nine people, including a two-year-old boy, have died in flash floods in New York and New Jersey following Hurricane Ida.
Dramatic footage shows water gushing into Manhattan subway station amid record-breaking rainfall.
Another clip shows water pouring over a subway train as it arrives in Brooklyn, with one commuter sprinting out of the carriage to safety.
Early reports said residents had lost their lives after becoming trapped in their basements.
Meanwhile a man in his 70s died after the vehicle he was travelling in was flooded with water in Passaic, New Jersey.
Firefighters managed to rescue two others from the vehicle and retrieved the elderly man's body.
Another person has also died in the New Jersey floods, reports say.
New York City residents have now been banned from driving on the streets until 5am.
Nearly all of New York City's subway trains have now been stopped amid the chaotic scenes.
The city's Mayor Bill de Blasio declared a state of emergency on Wednesday night due to the "historic weather event".
He said: "Please stay off the streets tonight and let our first responders and emergency services get their work done. If you're thinking of going outside, don't. Stay off the subways. Stay off the roads. Don't drive into these heavy waters. Stay inside."
Flash-flood emergencies have been issued for counties across New Jersey and New York.
The National Weather Service branch for New York said it is the first time a flood emergency warning has been issued for the city.
Under a flash flood emergency, people are urged to move to higher ground and to avoid flood waters at all costs.
The National Weather Service said: "Move to higher ground now. This is an extremely dangerous and life-threatening situation.
"Do not attempt to travel unless you are fleeing an area subject to flooding. Turn around, don't drown when encountering flooded roads.
"Most flood deaths occur in vehicles."
The unprecedented alert was issued while Manhattan's Central Park recorded its highest ever amount of rainfall in a single hour last night.
Thousands have been left without power after a state of emergency was declared.
City residents were seen to be fleeing as heavy rain and wind lashed the streets.
In one video a delivery driver appeared to be bravely persevering with a food order as he waded through a flooded street as water crept up nearly to his waist.
Another person was captured on video appearing to relax while lying on an inflatable lilo on a completely flooded city street.
Cars were recorded almost completely submerged in streets that were drowned in floodwater.
The flooding has been blamed on Hurricane Ida, which has now turned into a tropical storm.
The remnants of the hurricane are pushing north across the eastern section of America.
Tornadoes spawned by the storm ripped through parts of Pennsylvania and New Jersey.
It comes after Ida swept across Louisiana, causing chaos in the state.
Hundreds of thousands of people have been left without power after the hurricane, which also destroyed countless homes.
Ida came ashore as a Category 4 hurricane on Sunday, hitting the southern coastline.
The barrier island town of Grand Isle in Louisiana was declared uninhabitable by the parish president after it was covered by 3ft of sand.
Virtually every structure on the island of 740 people sustained damage and about 40% were destroyed.
Major marine vessels and dry docks were reportedly picked up and moved.
New Orleans was also battered by the hurricane, with looting breaking out during the chaos.
Police Chief Shaun Ferguson said: "This will not be tolerated. We have made arrests. This is a state felony and we will be booking you accordingly.
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"This is not the time to take opportunities of our vulnerable population right now. We all are vulnerable at this point in time."
Officers have deployed anti-looting teams across New Orleans in an effort to protect property.
The hurricane's death toll rose to six on Wednesday after it emerged two electricity workers in Alabama were electrocuted while repairing the power grid damaged by the weather.
