UPDATE (3/11/20): 

The Oriental Land Company has announced that the temporary closures of Tokyo Disneyland and Tokyo DisneySea will be extended through early April out of consideration for the health and safety for guests and cast members. As a result of this extension, the Grand Opening of the new areas of Tokyo Disneyland, previously scheduled for April 15, has now been postponed until mid-May 2020 or beyond.

ORIGINAL (2/27/20):

The Oriental Land Company (OLC) has announced they will be temporarily closing Tokyo Disneyland and Tokyo DisneySea from Saturday, February 29 through Sunday, March 15th. This is an effort to fight the spread of the Coronavirus. According to the Japan Times, this is in line with the government’s request to cancel or postpone big events for the next two weeks. OLC had previously taken steps including having Cast Members wear masks and reducing character meet and greets.

Both Shanghai Disneyland and Hong Kong Disneyland are also currently closed in an effort to stop the spread of the virus. Disneyland and Walt Disney World in the United States and Disneyland Paris in France remain open.

While the English version of the Tokyo Disney Resort Website has not yet been updated to reflect the closure, the Japanese language version has, and below is an image of the closure page translated by Google.