The prosecutor's office in the southern state of Oaxaca said Sánchez Cabrera was riding a motorcycle with another person on a rural road when gunmen opened fire on them.
There was no immediate information on the condition of the other person. The attack occurred in Oaxaca's isthmus region.
Local media and press groups said Sánchez Cabrera had complained of receiving threats and attacks in recent months.
Reporters Without Borders demanded “a thorough investigation into the threats and attacks that he had reported earlier related to his work as a journalist.”
At least two journalists have disappeared this year in the violence-wracked northern border state of Sonora, and in May, online journalist Benjamín Morales Hernández was abducted and killed in Sonora.
Morales Hernández ran an community news site called Noticias Xonoidag. His family reported he had been abducted and his bullet-ridden body was later found on a highway.
Press groups say nine journalists were killed in Mexico in 2020, the highest total of any country not at war.