CAMDEN, N.J. (CBS) – Authorities are investigating the cause of a two-alarm fire in Camden that sent three people to the hospital Friday morning.

The fire broke out at about 1:30 a.m. in the unit block of South 24th Street. When crews arrived, they discovered heavy smoke on the second floor of a vacant row home. Authorities say the fire quickly spread to two other homes, one of which was also vacant.

Three people were transported to Cooper University Hospital to be checked out for smoke inhalation and are expected to be okay.

There is no word on the cause of the fire at this time.