Hurricane Sandy has strengthened as it approaches the U.S. East Coast, putting some 50 million people in the path of torrential rain, high winds and dangerous tidal surges from one of the largest storms to hit the region in years.

Major U.S. cities from Washington to New York came to a standstill on Monday, with public transit systems suspended, airports closed and millions of people forced to stay home from work. Sandy's maximum sustained winds intensified to 150 kilometers per hour as it began a westward turn toward the U.S. mid-Atlantic Coast.

Forecasters say the storm is 65 kilometers south of Atlantic City, New Jersey — about 200 kilometers south of New York City — and traveling westward at 44 kilometers per hour.

President Barack Obama canceled election campaign events to monitor the storm from the White House. He urged those in the storm's path to heed warnings about the dangerous nature of it.

“The most important message that I have for the public right now is please listen to what your state and local officials are saying. When they tell you to evacuate, you need to evacuate. Do not delay, don't pause, don't question the instructions that are being given because this is a serious storm and it could potentially have fatal consequences if people haven't acted quickly.”

Authorities in nine U.S. states and Washington, D.C. declared states of emergency, as the storm has already knocked out power to 1.5 million people on the U.S. east coast. U.S. federal government offices were closed Monday and will remain so on Tuesday.

U.S. Coast Guard helicopters rescued 15 crew members who abandoned a tall ship after it started to take on water off the coast of the state of North Carolina. The Coast Guard says it is searching for one other crew member who is missing from the HMS Bounty. The replica of an 18th century ship was featured in the 1962 film “Mutiny on the Bounty.”

Weather forecasters say Sandy is expected to merge with a cold weather system, transforming it into a “super storm” before it makes landfall. New York authorities ordered the evacuation of 375,000 people from low-lying parts of the city, whose major stock markets were closed in their first unplanned shutdown since the 2001 terrorists attacks.

Officials say people who refuse to evacuate and later need to be rescued will be putting the lives of emergency workers at risk.

Sandy killed at least 65 people in the Caribbean last week before it moved toward the United States.