An expected rainfall of up to 100 millimetres has caused flooding and mudslides on several Vancouver Island roads.

Highway 18 in Cowichan Valley was briefly shut down both ways due to a mudslide, according to Mainroad South Island Contracting. Eastbound lanes reopened at around 3:45 p.m. and westbound lanes were expected to stay closed until 6 p.m.

A detour was in place via Cowichan Lake Road between Cowichan Lake and Skutz Falls. There was no estimated time of reopening for the highway, which connects the city of Duncan to the community of Youbou.

North of Parksville, Martindale Road was shut down in both directions because of flooding between Levirs Road and Turner Road.

Local detours were in effect and Drive BC said it would provide an update on the route's condition at 5 p.m.

On the west coast of the South Island, Pacific Marine Road was also closed due to flooding between Fairy Road and Fairy Lake one kilometre north of Port Renfrew.

A detour was in effect for that route, and an update was expected at 5 p.m.

Videos surfaced on social media of the Little Qualicum River near Qualicum Beach breaching its banks upstream from Highway 19A.

Dashwood Fire Department said about three inches of water was covering the road in the 5100-block of Highway 19A, and encouraged drivers to slow down.

Flood mitigation efforts and turbidity associated with the rainfall also prompted a boil water advisory for users of the Comox Valley Water System.

A high streamflow advisory is currently in effect for B.C.'s South Coast and west Vancouver Island, including tributaries around Tofino, Bamfield, Port Renfrew and surrounding areas.

Environment Canada issued weather warnings for most of Vancouver Island earlier in the day due to an intense front hovering over the region.

Rainfall warnings were issued for west Vancouver Island, inland Vancouver Island and Greater Victoria, and rainfall and wind warnings for east Vancouver Island.

Most regions except for Greater Victoria were forecast to receive upwards of 100 millimetres of rain.

On the east coast, a wind warning was also in effect for Courtenay to Campbell River and Nanoose Bay to Fanny Bay, with southeast winds of up to 70 kilometres an hour expected over exposed coastal sections.

Greater Victoria was expected to fare slightly better. Environment Canada said the region received 20 to 30 millimetres of rain overnight, and would receive an additional 20 to 30 millimetres of rain on Thursday.

The heavy precipitation is expected to taper off into showers once the frontal system leaves the region Thursday night.