A car bomb exploded at a police station in the coastal city of Kozhikode, killing two people, Kerala Police Commissioner Ramesh Kumar and another officer, police said.
Two men who were riding in a police vehicle were killed and a civilian was injured, a police official said.
The explosion happened at around 10:30pm local time (12:30am ET) in the parking lot of the police station on the main road to Kozhikkode, which has a population of some 8,000.
A police officer said one of the victims, a woman, died at the hospital.
Two other people were injured, the official said, adding that one of them was a police constable and the other a passenger in a car.
Kerala police had issued a “red alert” on Saturday after receiving a call reporting a suspicious car.
Police said they were trying to determine if the bomb was a suicide or a car bomb.
They said the two suspected attackers are believed to have fled the scene.
Police are investigating whether there was a political motive behind the explosion.