WASHINGTON — Thousands of commuters and travelers had to scramble Wednesday after a deadly Amtrak train derailment shut down a critical section of the busiest railroad in North America.

More than 2,200 trains a day — including Amtrak, commuter railways and freight — run through the Northeast Corridor, and the crash has choked the rail system.

Amtrak warned early Wednesday that there would be no service between Philadelphia and New York, and that service elsewhere in the region would have to be modified.

"There is no circumstance under which there would be any Amtrak service this week through Philadelphia," the city's mayor, Michael Nutter, said after viewing mangled tracks and downed wires at the crash scene.

Amtrak alone carries 11.4 million passengers a year through the Northeast Corridor, and many found themselves offloaded far from their destinations Wednesday morning.

Airlines added flights and bus lines said they would honor Amtrak tickets, but many travelers struggled to find seats.

"I've been standing here in a daze, trying to figure out what to do," Bill Atkins, 48, said at Penn Station in Manhattan. The attorney was trying to get home to Tysons Corner, Virginia, after a New York business trip, and didn't learn about the crash until he woke up Wednesday. "I'm going to try to fly," he decided.

But there were no flights available from LaGuardia or Kennedy, so he was thinking about taking NJ Transit as his next step. "I think I'm going to get to the Newark Airport and just stand in line."

Wednesday afternoon flights between New York and Washington quickly sold out on Delta Air Lines, which was considering adding flights and switching to larger jets in both directions, spokesman Anthony Black said.

American Airlines, which flies the other shuttle route through its US Airways brand, was monitoring the situation, but as of Wednesday morning, believed it had enough capacity, spokeswoman Andrea Huguely said.

Greyhound added 16 more scheduled trips between New York, Philadelphia and Washington, and said Amtrak customers can exchange their train tickets for seats on Greyhound buses until Amtrak service resumes.

At Union Station in Washington, dozens of people waited to talk with Amtrak agents as electronic boards showed all the trains to Boston and New York cancelled.

"We want to get home," said Wilhelmina Green, 66, who boarded a New York-bound train in South Carolina Tuesday night with her sister Dorothy Archbold-Wright, 68. They expected to arrive Wednesday morning, but were offloaded in Washington instead.

Several dozen others waited in other lines to get bus tickets as television screens showed images of the derailed train.

"My only disappointment with Amtrak is that they just leave you hanging," said Jane Scarfo, whose train trip from Florida to New York suddenly ended in Washington.

Several passengers complained that Amtrak didn't help them make alternative arrangements. Scarfo said she was eventually able to book a Greyhound bus for later in the day.

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Associated Press writer Karen Matthews in New York contributed to this report.