The new state of emergency will last until early May, Prime Minister Pedro Sanchez said in a televised speech.
“The situation we are going through is extreme,” he stressed.
The measures were agreed earlier Sunday at a two-and-a-half-hour cabinet meeting convened following calls from Spanish regions for the power to impose curfews themselves.
A government statement said the overnight curfew would run from 11pm until 6am, currently 2200 GMT to 0500 GMT.
While the state of emergency would initially last for just 15 days, the government planned to ask parliament to extend it for six months, the statement added.
Sanchez nonetheless said that if conditions allowed, the measures could be lifted earlier than anticipated.
“The state of emergency is the most effective tool to lower the rate of infection,” he argued.
On Wednesday, Spain became the first European country to record more than a million cases of the virus, and almost 35,000 people have died from it.
Authorities were responding to calls for help from 10 Spanish regions and the city of Melilla, the government statement said.
Under the state of emergency, the regions would have the power to limit movement in and out of their territories, and could also extend the curfew by an hour on either end depending on local conditions.
Spain was locked down during an initial state of emergency that lasted from March 15 to June 21, and the measures were among the strictest anywhere in Europe.
Sanchez said that he sought “at any price” to avoid a second severe lockdown.
“Let's stay home as much as possible,” he urged in the television address.
“The more we stay home the more protected we and others will be.”