The crash was reminiscent of the problems that plagued the Affordable Care Act’s online health insurance exchange under President Barack Obama. It came on a day when President Trump and his top advisers were trumpeting the $1.5 trillion tax cut passed by Congress late last year.
Treasury Department officials had no comment, but the I.R.S. acknowledged that the agency’s systems are experiencing technical difficulties.
The outage comes as Republican lawmakers have been mulling legislation to restructure the I.R.S. and after years of depleted budgets for the agency. The passage of the new tax law has put an additional strain on the I.R.S. as it attempts to issue new guidance and regulations to clarify lingering questions about the tax code overhaul Mr. Trump signed into law.
The failure of the I.R.S. website drew fierce criticism on social media, with taxpayers berating the agency.
“There’s no greater example of government incompetence than the IRS e-file system and direct pay service being down on #TaxDay,” Joe Walsh, the former Republican congressman and conservative radio host, wrote in a post on Twitter.
Republicans have been trying to sell the new tax law to the public as a major success ahead of November’s midterm elections. Steven Mnuchin, the Treasury secretary, traveled to New Hampshire with Ivanka Trump, the president’s daughter and senior adviser, on Tuesday to hail the success of the tax overhaul.
Despite the balky website, Mr. Kautter said on Tuesday that the agency had much to be proud of this year.
“This year’s tax season is an example of what the I.R.S. must do more of going forward, delivering for the nation’s taxpayers,” he said.
Larry Kudlow, the president’s new head of the National Economic Council, joked about the outage with reporters during a briefing in Mar-a-Lago, the president’s Florida estate, where Mr. Trump is meeting with Japan’s prime minister.
“Sounds horrible. Sounds really bad. Hope they fix it,” Mr. Kudlow said. He later returned to the topic on a more serious note, saying he was confident the I.R.S. would rectify the issue and saying that the 2017 tax overhaul would simplify filing for everyone going forward.