SIX people who were aboard a commercial charter vessel that sank on Sunday near Richmond remain missing, Richmond RCMP said on Monday.

Despite extensive multi-agency search efforts conducted on Suinday, four men and two women remain unaccounted for and are presumed drowned. The search has been suspended, and efforts have now shifted to recovery.

The RCMP Underwater Recovery Team (URT) has been engaged and will attend the area in the coming days to locate the capsized vessel using sonar. Their assessment of the conditions will determine whether a dive operation is feasible, or whether alternate resources, such as a remotely operated vehicle (ROV, aka underwater drone), may be required.

The vessel is believed to have sunk in very deep waters.

The investigation remains ongoing to determine the cause of the sinking and to confirm the identities of the six missing individuals. Efforts are also underway to notify their respective next of kin.

A 26-year-old man and a 33-year-old woman have since been discharged from hospital. A 33-year-old man and a 28-year-old woman both remain in critical condition.

Police are working closely with Transport Canada, the Transportation Safety Board and other partner agencies to support the investigation and coordinate next steps.

The BC RCMP said on Sunday that the vessel began taking on water near Roberts Bank around 11:45 a.m. The incident was reported by another civilian vessel and a marine search and rescue operation was launched by the Joint Rescue Coordination Centre Victoria. The search has involved several agencies including the RCMP, the Royal Canadian Air Force, Canadian Coast Guard, Royal Canadian Marine Search and Rescue, and BC Ferries.

The search included vessels as well as aircraft. The RCMP had two boats from West Coast Marine Services, the P.V. Lindsay and P.V. Higgitt, assisting, as well as two helicopters, an RCMP Black Hawk and an H145 Airbus from RCMP Air Services.