Armando Linares, director of the local website Monitor Michoacsn, said three assailants fatally shot Roberto Toledo in the city of Zitacuaro.
Prosecutors in the western state of Michoacan said they were investigating the report.
Linares said the website had received threats for reporting on governmental corruption.
"For exposing corrupt administrations and corrupt officials and politicians, today that led to to death of one of our colleagues," said Linares.
"There people came up to him and shot him."
"The Monitor Michoacan team has suffered weeks, months of death threats. We know where all of this comes from," Linares added, though he did not identify those he thought responsible.
Jan-Albert Hootsen, the Mexico representative for the Committee to Protect Journalists, said Toledo worked as a camera operator and video editor for the Monitor Michoacan.
"We are classifying him as a media worker or press worker," Hootsen said.
Toledo was filming a new video column by Monitor Michoacan's deputy director, Joel Vera, a local lawyer, at Vera's office when the gunmen arrived, the outlet said.
Jesús Ramírez, spokesman for President Andres Manuel López Obrador, said via Twitter that the administration condemned Toledo's killing.
"We will work together with the state and municipal governments to clear up the case," Ramírez wrote.
"We will not allow impunity. We defend freedom of expression and the right to information."
The unprecedented spate of killings has put reporters on edge across Mexico, and sparked protests earlier this month. The government said over 50 journalists have been slain in Mexico since December 2018.
In the border city of Tijuana, two journalists were killed in the space of a week. On January 17, crime photographer Margarito Martínez was gunned down outside his home.
On January 23, reporter Lourdes Maldonado Lopez was found shot to death inside her car.
Reporter Jose Luis Gamboa was killed in the Gulf coast state of Veracruz in an attack on January 10.
Interior Undersecretary Alejandro Encinas said recently that more than 90 per cent of murders of journalists and rights defenders remain unsolved, despite a government system meant to protect them.
The New York-based Committee to Protect Journalists puts the percentage at 95 per cent, said its Mexico representative, Jan-Albert Hootsen.
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