On Sunday, reporters at the Perthus crossing near the eastern end of the border saw cars crossing both ways every two or three minutes, with more going from Spain into France.
There were no checks from midnight and the traffic flowed freely.
The Spanish government announced on Saturday that from Sunday EU member state citizens and those from the passport-free Schengen zone would be allowed freely into Spain, with no 14-day quarantines required.
However, Portugal has said it will keep its border with Spain closed until July 1.
With the state of emergency lifted, Spaniards were also allowed to travel outside their home region for the first time since the lockdown was imposed on March 14.
“I am a little afraid to travel, I remain cautious,” said Alba Bartolome, 22, who was waiting for a train to Murcia from Madrid’s main Atocha station.
In the “new normal”, Spaniards will have to wear masks in enclosed spaces, maintain social distancing of 1.5 metres while access to pools, beaches, hotels and restaurants will be limited accordingly.
About 600 health ministry staff meanwhile will monitor airports to check the personal details and temperature of arriving foreign passengers.
Doctors will examine any suspected cases.
Sanchez had warned Spaniards on Saturday not to let their guard down.
“We are still vulnerable. We have to be careful and follow strictly the health measures,” he said.
From July 1, Spain will fully open all its borders.