One Canadian military member is dead and five others are missing after a helicopter serving with a NATO naval task force crashed in international waters between Greece and Italy on Wednesday, Prime Minister Justin Trudeau confirmed today.

Four Royal Canadian Air Force members and two Royal Canadian Navy members were on board at the time.

"All of them are heroes. Each of them will leave a void that cannot be filled," Trudeau said.

Nova Scotia Sub-Lt. Abbigail Cowbrough, a marine systems engineering officer originally from Toronto, is confirmed dead.

Later on Thursday, the defence department identified those still missing:

Capt. Brenden MacDonald, a pilot originally from New Glasgow, Nova Scotia.

Capt. Kevin Hagen, a pilot originally from Nanaimo, British Columbia.

Capt. Maxime Miron-Morin, an air combat systems officer originally from Trois-Rivières, Québec.

Sub-Lt. Matthew Pyke, a naval warfare officer originally from Truro, Nova Scotia.

Master Cpl. Matthew Cousins, an airborne electronic sensor operator originally from Guelph, Ontario.

Clockwise from top left: Capt. Kevin Hagen, Sub-Lt. Abbigail Cowbrough, Capt. Brenden Ian MacDonald, Master Cpl. Matthew Cousins, Sub-Lt. Matthew Pyke, Capt. Maxime Miron-Morin. (Department of National Defence)

Trudeau acknowledged that today is another "very hard day" for Nova Scotia — still grieving the victims of a gun massacre — and for all Canadians.

The six members were on a six-month deployment that began in January.

There will be many questions in the coming days about how the tragedy occurred, Trudeau said.

"I can assure you, we will get answers in due course."

Ships from Canada, Italy and Turkey, with air support from Greece and the U.S., are searching for the CH-148 Cyclone helicopter.

Rear Admiral Craig Baines, Commander, Maritime Forces Atlantic, thanked allies for their "steadfast" support as he provided an update on rescue efforts late Thursday.

Watch: Royal Canadian Navy maritime commander provides update on search efforts

Rear-Admiral Craig Baines, commander of Maritime Command Component, says searchers have found debris from the crashed helicopter but it's still "too early to know what happened." 0:45

Baines said the search will continue through the night. He said weather conditions have been good so far, but the process becomes more challenging as the search area widens.

"A search on the ocean is always very difficult, even in relatively calm conditions. Very small objects in the water are very difficult to find over long periods of time as wind and current expands the search area," he said.

"So even in perfect conditions it is a difficult thing to do a search on the water. But they are continuing, and they will continue to search as long as they still believe there is an opportunity to find survivors."

Baines said some debris related to the chopper has been found but it's too early to say what may have happened.

Watch: Trudeau responds to Canadian military helicopter crash near Greece

Prime Minister Justin Trudeau confirms that a military helicopter on a NATO mission that crashed off the coast of Greece was carrying six members of the Canadian Armed Forces. 1:55

Chief of the Defence Staff Gen. Jonathan Vance said the Cyclone fleet has been put on "operational pause" temporarily to allow flight safety teams to investigate and rule out any fleet-wide problems. He added the helicopter fleet is modern and has "state-of-the-art" technology.

"We have a lot of confidence in this fleet," he said.

"These are ... superbly trained crews, pilots, electronic systems operators and so on. It's a powerful helicopter with fantastic sensing capability and it's about to go through a second block of upgrades to integrate that sensing capability."

Location of wreckage not known

Vance said the crash's debris area is large and the exact position of the wreckage is not yet known. The cockpit voice and flight data recorders broke away from the helicopter with a beacon and have been retrieved, he said.

They will brought to the National Research Council for analysis.

Vance said the helicopter was returning to HMCS Fredericton when it crashed. At about 6:52 p.m. local time, the ship lost contact with the air crew. A few minutes later, automatic flares were spotted in the water.

"This is a time of agony for all families, friends, and fellow crew members. There is nothing worse than sending your shipmates over the horizon and losing contact," he said.

Watch: Gen. Jonathan Vance provides details on the fatal navy helicopter crash

Chief of the Defence Staff General Jonathan Vance spoke to reporters on Parliament Hill on Thursday. 3:56

Vance said the goal of the operation is to warn Russia and other adversaries not to interfere with European or North Atlantic security, and to assure allies "that we are all in this together."

At the time of the accident, the group was conducting training – not surveillance or targeted operations, he said.

"We can't rule anything out, but I'm quite certain from a military situation, this was not a function of contact or a shootdown. I want to make that abundantly clear," he said.

Cause of crash unknown

Defence Minister Harjit Sajjan said the cause of the crash remains unknown.

"I've had a number of conversations with the secretary general of NATO. We remain in contact with Italy, Greece, the United States and Turkey, who are assisting us in the search and rescue efforts to help us find the Canadian Armed Forces members who were on the helicopter," he said.

Sajjan said an investigative team is en route to the region to get answers.

The helicopter was based on HMCS Fredericton, which recently sailed from Souda, Greece, as part of a "mission of maritime situational awareness in the Mediterranean," including exercises with the Turkish Navy and Greece's Hellenic Navy and Air Force this past week, NATO said.

"As announced, 1 CAF member is deceased & 5 missing following a helicopter crash in the Ionian Sea. On behalf of the entire CAF I send our deepest condolences to her family, friends & shipmates. May her memory be a source of comfort & inspiration to us all. We will remember." JV <a href="https://t.co/liB5KFnBgE">pic.twitter.com/liB5KFnBgE</a> —@CDS_Canada_CEMD

Vance said the military has been in touch with next of kin.

"In a season of grief – a time of hardship, heartbreak and loss for so many Canadians – the men and women of the Canadian Armed Forces stand tall," he said. "Bearing the maple leaf on their shoulders, they are known around the world as beacons of civility, compassion and courage."

The search continues for five Canadian military members and the navy helicopter they were on that crashed in international waters between Greece and Italy Wednesday. (Turkish Ministry of National Defence/Twitter)

Conservative Leader Andrew Scheer expressed his condolences to family members and the military community.

"Any loss of life within Canada's proud military is a tragic event, one that is deeply felt by all Canadians. I don't doubt, though, that this loss will be particularly difficult for Nova Scotians, as HMCS Fredericton is based out of Halifax," he said in a media statement.

"I would like to thank all the men and women serving during Operation Reassurance, Canada's largest current international military operation, who are helping make Central and Eastern Europe more stable and secure."

The Canadian Forces has confirmed contact was lost with a Canadian CH-148 Cyclone helicopter taking part in NATO operations in the Mediterranean. (CBC News)

NDP Leader Jagmeet Singh said he's saddened by the news and sends his love and support to the family and friends of Cowbrough and the missing military members.

NDP defence critic Randall Garrison called it "devastating" news for the military community and for all Canadians.

WATCH | Nova Scotia naval officer dead, 5 missing after helicopter crash near Greece:

Sub.-Lt. Abbigail Cowbrough, 23, has been confirmed dead and five members of the Halifax-based crew are missing after a military helicopter crashed near Greece on Wednesday. The five people still missing are Capt. Brenden MacDonald, Capt. Kevin Hagen, Capt. Maxime Miron-Morin, Sub-Lt. Matthew Pyke and Master Cpl. Matthew Cousins. 2:06

"Today, we mourn the loss of Sub-Lt. Abbigail Cowbrough and send our support to her family during this difficult time. To the families of those still unaccounted for: You are in our thoughts. We're hopeful that the investigation into this tragedy happens quickly and efficiently so that you can have the answers you need," he said.

Lt-Gen. Al Meinzinger, commander of the Royal Canadian Air Force, and Vice-Admiral Art McDonald, commander of the Royal Canadian Navy, issued a joint statement Thursday afternoon,

"There are no words to describe a loss as tragic as this," the statement reads.

"This incident serves as a difficult reminder of the sacrifice that our brave men and women face daily while defending and representing our nation, both at home and abroad.

"It also serves to remind us all how dangerous even routine operations at-sea and in the air can be. In the face of these realities, the sailors and aviators aboard Navy frigates operate as one team – one family – a family that today mourns together."

Greece expresses grief

Greek Prime Minister Kyriakos Mitsotakis spoke about the crash in the nation's parliament Thursday.

"I express my grief over the crash of the Canadian helicopter in the Ionian Sea last night," he said.

Mitsotakis said he would contact Trudeau personally to express his condolences.

Watch: Gen. Jonathan Vance describes the emotional impact of the Cyclone crash on serving members

Chief of the Defence Staff Gen. Jonathan Vance spoke about a "time of agony" for the Canadian Armed Forces and family members of those who were on board the military helicopter that crashed off the coast of Greece. 0:56

The crash occurred in the Ionian Sea about 80 kilometres off the Greek resort island of Cephalonia.

The Cyclone is a militarized version of the Sikorsky S-92 utility helicopter.

The Cyclones replaced the air force's five-decade-old CH-124 Sea Kings, which were gradually retired from service over the last few years. The crash of a Cyclone represents a major blow, given how long the military had to wait for the aircraft to be developed.

Cost escalations

Originally ordered in 2004, the Cyclone program faced delays and cost escalations — to the point where former auditor general Sheila Fraser slammed the federal government's handling of the project in 2010.

The Cyclone routinely flies with a crew of four: two pilots, a tactical operator and a sensor operator. It also has room for several passengers. The helicopter's primary mission is hunting submarines, but it has a sophisticated surveillance suite and is also outfitted for search-and-rescue.

HMCS Fredericton had recently sailed from Souda, Greece. (The Canadian Press)

Since coming into service, the Cyclone has been deployed on five overseas missions with the navy, including previous NATO stints.

The air force has praised the aircraft's capabilities repeatedly — although it was involved in at least one shipboard accident while serving with HMCS Regina and the resupply ship MV Asterix in the Pacific Ocean last year.

A Cyclone suffered what defence officials described at the time as a "hard landing" aboard the Asterix on Feb. 18, 2019.

Vance said today that incident was caused by a strong gust of wind, not a mechanical issue.