The Spanish government says the number of migrants arriving in the Canary Islands from Africa was 18 times higher last month than in the previous January.
The interior ministry said 708 migrants arrived, compared to 40 the year before.
The rise coincides with a decline in the numbers arriving in mainland Spain from Morocco, as the authorities there have stepped up efforts to prevent illegal crossings.
Migrants can reach the Canary Islands direct from Mauritania or Senegal, thereby avoiding the Moroccan authorities.
In 2019 the European Union allocated more than $150m (£115m) to Morocco to halt illegal migration.