The IRS did not give an immediate explanation for the failures but said in a statement that "certain IRS systems are experiencing technical difficulties".
"Taxpayers should continue filing their tax returns as they normally would", said Bruce Friedland, an I.R.S. spokesman. The full extent of the website failure was not immediately known.
While you can send in a physical form to file that extension, there are also a number of web services available that can let you file that extension from your desk without braving the post office lines (your extension needs to be postmarked for today in order to count).
Acting Commissioner David Kautter acknowledged the issue Tuesday morning in a House Oversight Committee hearing.
The IRS also has payment plans available for those who can not afford to pay their taxes in full at the deadline, but you will be subject to interest payments and fees. An IRS spokeswoman would not comment on when the problem would be resolved.
For taxpayers who use software to file their returns, it's also possible to pay through the tax filing service itself.
Eldorado Resorts to Acquire Tropicana Entertainment for $1.85 Billion
Icahn Enterprises said it plans to sell the Aruba resort before closing on the Eldorado/Gaming deal by the end of the year. In Atlantic City, Icahn still owns the shuttered former Trump Plaza Hotel and Casino, which shut down in 2014.
Trump's top economic adviser Larry Kudlow offered a deadpan reaction when asked about the failure.
The IRS typically recommends that taxpayers use electronic filing to avoid common mistakes.
An IRS website reported at midday Tuesday that the agency's Modernized eFile System was down. "Given this news, I hope that the IRS will make accommodations so that every taxpayer attempting to file today has a fair shot to do so without penalty".
Congress approved $320 million in short-term funding to help the agency implement the new tax law as part of the massive budget deal it passed in March, but many lawmakers say more funding is needed.
"This is game-day for the IRS, and it seems the IRS can't get out of the locker room", said Rep. Greg Gianforte (R-Mont.).
The IRS discovered the problem early Tuesday morning, Kautter said, and it plans to attempt a "hard reboot" of its system in an effort to address the failures.