Director Avelino Razon, head of the PNP Directorate for Operations, said Comelec control of the entire Masbate province, which has 12 municipalities, was also recommended to the poll body.
Razon said the four cities are San Carlos in Pangasinan, Ligao in Albay, Santiago in Isabela and Masbate in Masbate.
The 51 towns declared election "hot spots" are in the provinces of Abra, Kalinga, Ilocos Sur, Ilocos Norte, Pangasinan, Masbate, Albay, Cagayan, Isabela, Zamboanga del Sur, Zamboanga del Norte and Zamboanga Sibugay.
Razon said the PNP based its recommendations on the intense political rivalries, big number of poll-related violent incidents and the presence of communist rebels, among other factors, in these areas.
Meanwhile, the PNP has tagged 44 towns and cities as "areas of immediate concern" and 579 others, 12 of them in Metro Manila, as "areas of concern."
Since the campaign season began last Dec. 15, the PNP has recorded 82 poll-related violent incidents that left at least 70 people dead and 137 others wounded.
The PNP said 163 members of partisan armed groups have been arrested nationwide.
The Comelec has deputized the PNP and the Armed Forces to guard the 239,824 polling precincts nationwide.