An equipment failure on a BC Ferries vessel Friday morning caused two staff members to fall into the water from a "significant height," according to the ferry workers' union.

The BC Ferry and Marine Workers' Union issued a news release saying the issue was with a piece of equipment called a davit on the Spirit of Vancouver Island.

The extent of the workers' injures is unknown, but the union said it expects investigations by BC Ferries Services, WorkSafe BC and the Transportation Safety Board.

The incident prompted BC Ferries to cancel four sailings between Tsawwassen and Swartz Bay: the 7 and 11 a.m. sailings from Swartz Bay, and the 9 a.m. and 1 p.m. sailings from Tsawwassen.

It's caused massive travel delays ahead of the busy Labour Day long weekend, with BC Ferries reporting a three-sailing wait from Swartz Bay to Tsawwassen. As of 12:45 p.m., the next available ferry from Swartz Bay was at 5 p.m., and the next available ferry from Tsawwassen was at 6 p.m.

BC Ferries apologized to travellers for the inconvenience and said it would schedule an additional sailing from Tsawwassen to Swartz Bay at 11 p.m. Just before 1 p.m., it said there appeared to be no delays for walk-on passengers.

It also said on Twitter that travellers who held reservations for later sailings would not be bumped.

The president of the ferry workers union said he's concerned because a similar issue with a rescue boat caused injuries to workers earlier this year.

“This is the second time this year there has been a substantial failure regarding rescue boats, and these incidents cause our Union deep concern,” said Graeme Johnston.

In April, two workers conducting a rescue boat drill on the Queen of Cumberland at Swartz Bay also fell into the water, suffering non-life threatening injuries.