Reuters images showed rocks falling violently and clouds of white steam billowing up from the Playa Nueva area. Officials had warned of possible explosions and clouds of toxic gases when the lava reaches the sea.
"When the lava reaches the sea, the lockdown must be strictly observed," Miguel Angel Morcuende, director of the Pevolca response committee, said earlier on Tuesday.
Lava has been flowing down the volcano's western flank toward the sea since Sept. 19, destroying almost 600 houses and banana plantations in La Palma, which neighbors Tenerife in the Canary Islands archipelago off the North African coast.
Thousands have been evacuated and three coastal villages were locked down on Monday in anticipation of the lava meeting the Atlantic Ocean.
Spain classified La Palma as a disaster zone on Tuesday, a move that will trigger financial support for the island.