A loud explosion rang out near the 1000 block of South Amphlett Boulevard just after 7 a.m., police said.
Police and firefighters arrived and found an incendiary device -- similar to an M-80 firecracker -- that had been ignited near an abandoned couch in front of a vacant building.
The business sustained two broken windows caused by the blast, which was reportedly heard within a half-mile radius.
No injuries were reported.
The surrounding area was cordoned off for about two hours while a San Mateo County bomb squad responded to ensure that no other explosive devices were in the area.
San Mateo police and fire departments are continuing to investigate the incident.
