Two men drowned and eight others, including two children, were injured when a sailboat capsized Sunday evening in San Diego Bay.

The boat, initially reported to be a 35-foot rental, ran into unknown trouble shortly after 5 p.m. near Harbor Island. It was not immediately clear why the boat overturned, said Marguerite Elicone, a spokeswoman for the San Diego Port Authority, which oversees Harbor Police who are conducting an investigation into the incident.

San Diego Fire-Rescue spokesman Maurice Luque said there was no immediate indication that another boat was involved in the incident. Elicone said weather conditions had been fairly mild Sunday, though winds can kick up in the area in late afternoon.

The most seriously injured was a woman who remained in the intensive care unit at the University of California-San Diego Medical Center, where she was being treated for hypothermia, Elicone said.

All 10 people on board were in the water when Harbor Police arrived a few minutes after the incident.

Most of the victims were members of one family, Luque said. Identities of the two men killed were not released, but both were described as being in their 50s or 60s. Both were pronounced dead at a rescue command center on nearby Shelter Island, where 60 emergency workers received the victims from rescue boats, Luque said.

The injured children appeared to be about 10 to 12 years old, Luque said. The survivors were taken to Scripps Mercy Hospital, as well as the UCSD facility.

Most of the survivors were in stable condition Sunday night, and some, including one of the children, had been released.

Officials said they did not know whether the boat was under sail or running on its engine when it capsized.

Divers remained in the water Sunday evening, examining the boat as part of the investigation into the cause of the accident.

Luque said based on conversations with rescued family members, who were Asian and required some translation assistance, officials were confident they had accounted for everyone on the boat.