According to reports from Quezon City Police District (QCPD) Station 10, the explosion occured along Edsa Avenue near Barangay (village) Immaculate Concepcion at around 9 p.m.
The victims were identified by Senior Police Officer 3 Arvin Dimalig, QCPD Explosive Ordnance Division, as Rommel Simporios, 26, Manuel Melano, Catherine Esquivel 36, Nino Espina, 24, and Felicidad Orencio, 21.
The injuries they received in different parts of their body were due to fragments from an alleged grenade, police said.
A witness, identified as Frederick Penol, told the police that the victims were busy working inside the Everest Lumber store when the explosion occurred.
Police suspect that an old grudge between the vendors was the motive as one of them was mauled a few days prior to the incident.