Spain's state of emergency in place since October to fight the pandemic expired at midnight on Sunday.
Restrictions easing now allow Spaniards to travel to other regions for the first time in months.
In many regions, the lifting of the state of emergency also meant the end of local night-time curfews.
In Barcelona, hundreds of young people celebrated with dancing and singing at an improvised party held at the city's seaside.
In Madrid, police had to usher revellers out of the central Puerta del Sol square, where the scenes of unmasked dancing and group signing resembled pre-pandemic nightlife.
But some regional chiefs fear that the national state of emergency will be replaced by a patchwork of conflicting approaches.
The government has handed full control of the battle against COVID-19 to the country’s 19 regions and autonomous cities.
Regions can still restrict opening hours and impose capacity limits in bars and restaurants.
They can also seek court approval for stricter measures such as reimposing curfews, capping the number allowed at home gatherings or extending a ban on internal travel.
But the courts have offered different rulings, leading to a patchwork of measures across the country.
A court in the eastern Valencia region approved a midnight-to-6:00 am curfew, while the top court in the northern Basque Country said the area could not keep its nighttime curfew.
To avoid this scenario, several regions have lobbied Prime Minister Pedro Sanchez's government to extend the emergency.
But his administration has refused, arguing the measures could not remain in place indefinitely, pointing out that the infection rate was stable and that Spain's vaccination drive was progressing rapidly.
Even so, it passed a decree allowing regions the right to appeal to the Supreme Court if a local court strikes down a proposed measure.
Spain is one of Europe's hardest-hit nations with nearly 79,000 coronavirus deaths and 3.5 million infections.