A 22-year-old Greenport woman swerved into oncoming traffic and struck two other vehicles on Sound Avenue in Mattituck just after midnight Sunday, Southold Town Police said.
All five people involved in the 12:11 a.m. accident were taken to Eastern Long Island Hospital for unspecified injuries.
It was not clear what caused the driver to cross from the eastbound to westbound lanes in her 2006 Dodge, and no charges were listed in a police press release issued later.
She struck two other vehicles, a 2014 Jeep operated by a New Jersey man, and a 2003 Dodge that was being driven a Jamesport man.
Two passengers were also involved in the crash.