Airfares between New York and Washington, DC, have taken off since the fatal Amtrak derailing — with some round-trip flights going for four times the normal amount.

With rail service suspended at least until Monday, travelers have been scrambling to grab tickets on the busy, popular route.

American Airlines on Friday morning offered the few seats left on round-trip flights for as much as $1,000 leaving Saturday and returning Monday.

Prices on US Airways’ website hovered above $770, with many seats sold out even on connecting flights.

Fares on Delta Air Lines were more down to earth, with prices of about $530.

Travel sites Orbitz and Expedia didn’t offer any amazing deals, either — with fares ranging from $550 to $642.

Normally, round-trip flights between New York and DC cost about $200 for a regular ticket and as much as $600 for a last-minute flight, CNN reported, citing experts in the industry.

The sky-high fares posted Thursday went down a bit Friday, but were still not back to normal, said George Hobica, president of Airfarewatchdog.com.

“It could be because of the negative publicity. Maybe (the airlines) have been shamed,” Hobica told The Post.

He theorized that the slightly lower prices were due to lower demand ahead of the weekend — or added flights by the airlines.

Hobica — who recalled the halcyon days of $19 fares on Eastern Shuttle and People Express — said carriers can change pricing based on demand.

“Many of the passengers are business people traveling on economy, and their companies wouldn’t raise an eyebrow,” he said about the spike in fares.

Jenna Arnold, an American Airlines spokesman, said in an email that the airline didn’t change its pricing in the route this week.

The airline this week added two round-trip flights between LaGuardia Airport and Washington’s Reagan National Airport.

Delta and US Airways didn’t immediately respond to requests for comment.

A Delta spokeswoman told CNN on Thursday that it had added two more 76-seat flights each way due to an increase in bookings. It said it had not hiked prices after the accident, International Business Times reported.

United told CNN that the airline hadn’t added flights despite an increase in demand.

For those with more time — and less money — bus companies have added service along the route due to a sharp uptick in demand.

Greyhound and its BoltBus branch have added six buses, spokeswoman Lanesha Gipson said.

Round-trip tickets are still available for $79.50 on Greyhound, which is honoring Amtrak tickets, she said.

Megabus has added four buses along the route and also is honoring Amtrak tickets through the weekend, based on seat availability, spokesman Sean Hughes said.