At least one person has been killed and another four injured in a suspected terror attack on two churches in Spain.

Eye witnesses say that the alleged attacker shouted "Allahu akbar" and "death to Christians" during the machete attack on San Isidro Church and Nuestra Senora de La Palma Church in the southern Spanish city of Algeciras on Wednesday evening. 

The victim has been named in local media reports as Diego Valencia, a verger at the Nuestra Senora de La Palma church.

Valencia is reported to have been killed as he tried to stop the attacker, who entered the church as Mass was taking place.

Antonio Rodriguez, parish priest at the San Isidro Church, is reported to have been stabbed after the attacker tried to force him to convert to Islam. The priest is in hospital in serious condition.

Francisco Garcia, secretary general of Spain's Episcopal Conference, told Reuters that he was in "great pain" over the attack.

"These are sad times of suffering; we are united by the pain of the victims' families and for the Cadiz Diocese," he said.

A 25-year-old Moroccan has been arrested in connection with the attack.