All venues with alcohol licences in Guernsey that do not serve food will be closed from 18:30 GMT, the States says.
It follows a decision to close island schools due to delays in obtaining coronavirus test results from the UK.
The temporary ban on pubs, bars and nightclubs will be reviewed in 10 days, according to the States.
Restaurants and pubs that do serve food can remain open, but are only allowed to serve alcohol to dining customers sitting at tables.
The government also revealed the island's second confirmed case of Covid-19, in a patient who arrived from France.
It said the decision to close alcohol-only venues was part of a "pause-and-assess strategy", until "timely testing" for the virus could be resumed.
It is hoped on-island testing will possible by April, which could allow for the restriction to be lifted.
President of the Policy and Resources Committee Gavin St Pier said the "extent coronavirus may be spreading in our community" had become "less clear" due to delays to test results.
"We will not take any chances. Bars and clubs present a very real risk.
"This will come at very short notice to licensees but we will not make apologies for taking swift action to protect our community. This is a fast-developing situation and we are having to react in real time," he added.
The island banned all "non-essential travel" on Thursday and ordered all new arrivals to self-isolate for 14 days.