"We made the unprecedented decision to shut down ALMA for the well-being and health of all staff, to ensure they can be at home with their families while this pandemic unfolds.
"An incredible effort was made by staff to ensure a safe and successful shutdown," Xinhua news agency quoted ALMA Director Sean Dougherty as saying in the announcement on Thursday.
He added that "a team continues working at the observatory to keep vital telescope systems operational and ensure that we are ready to restart operations whenever that is feasible".
ALMA shut down on March 22 and was expected to resume operations no sooner than May 19, according to the announcement.
ALMA is an astronomical interferometer of 66 radio telescopes located in the Atacama Desert in northern Chile.
Chile's Health Ministry said 2,738 people have tested positive for the novel coronavirus and 12 have died so far.