The Cumbre Vieja volcano started erupting on Sunday with thousands evacuated and more than 350 homes destroyed.
On Friday, authorities in three more towns told residents to evacuate.
A thick plume of smoke now extends four kilometres (2.4 miles) into the air with a number of flights in and out of the airport cancelled.
No fatalities have been reported.
Volcanic activity increased on Friday and Spanish media is reporting that a new vent has opened up, causing lava to flow.
The firefighters had been conducting preventative work in Todoque neighbourhood.
Some 1,000 people in Tajuya, Tacande de Abajo and Tacande de Arriba were told to evacuate on Friday due to the intensifying volcanic activity.
Local flight operator Binter said it had cancelled all flights to La Palma due to the eruption, with Spanish airline Iberia also halting operations in the area.
The Canary Islands government has already announced a first round of financial aid for people who have lost their homes.
The volcano lies in the south of La Palma island, which is home to around 80,000 people.
It last erupted 50 years ago, in 1971. Scientists are unsure how long this eruption will last.
A spokesperson for Spain’s National Geographic Institute told the BBC that past eruptions on La Palma have lasted between 24 and 84 days.