Officials from the Transportation Safety Board and Transport Canada will speak to WestJet to find out why a Thursday evening flight dramatically plunged 300 metres, injuring nine passengers.

After the flight landed safely at Halifax Stanfield International Airport shortly before 7:30 p.m., three passengers were taken to hospital by ambulance and six others were treated at the scene. The passengers taken to hospital were released later Friday.

Mike Cunningham of the Transportation Safety Board said the independent agency will seek more information from WestJet in order to assess whether an investigation into the incident is needed.

Cunningham said turbulence isn't unusual, noting if the airline and flight crew followed proper procedure, an investigation would be unlikely.

Transport Canada spokeswoman Lucie Vignola said the federal agency will review the incident and determine whether proper procedures were followed.

Thrown like rag dolls

Passengers on the flight from Calgary to Halifax said people standinginside the plane's cabin were thrown around like rag dolls whenit hit turbulence about 330 kilometres north of Sudbury, Ont.

Hospital officials would not divulge the condition of those brought in,but a nurse aboard the flight said one man had bad lacerations to his head and leg.

Passengers say the pilot warned about the turbulence on the intercom, but many didn't have time to secure their seatbelts when, seconds later, the plane dropped straight down.

"All of the people rose up in their seats to where they had just been and hit their heads on the roof," passenger Scott Lacroix, 30, told the Halifax Chronicle Herald.

Two nurses aboard the flight helped those at the back of the plane, where the most serious injuries seemed to have been suffered. Two passengers had serious cuts, while a number of others were experiencing neck and back pain, the nurses said.

"There was one gentleman who had a really bad laceration to his head and his leg," nurse Kathi Nelson said.

The man had fallen on top of his wife, hurting her as well, said Nelson.

An Environment Canada meteorologist said thundershowers may have caused the turbulence.

With files from the Canadian Press