At least 23 people were killed as remnants of Tropical Storm Ida unleashed dangerous flash floods and tornadoes across the northeast U.S., according to local media.

Nine deaths, including a 2-year-old toddler, were reported in New York City, while the remaining casualties were from New Jersey.

Both New York and New Jersey have declared a state of emergency because of severe weather.

Operations of nearly all New York City subway lines were suspended since late Wednesday due to what New York City Mayor Bill de Blasio called a "historic weather event."

An overnight travel ban in NYC has been lifted. Still, officials urged people to remain indoors as emergency workers begin to clear up.

"Stay home as much as possible today until conditions improve," Mayor Bill de Blasio's office tweeted.

Earlier in the night, New Jersey Governor Phil Murphy also urged residents to stay off the roads and stay home, as he vowed to use every resource at his disposal to ensure the safety of New Jerseyans.

Murphy said the state will send a "major disaster declaration request" to the federal government.

Some 370 flights were temporarily halted in Newark Airport after severe flooding across New Jersey.

Heavy rainfall from Ida has also affected play at the U.S. Open.