Several slow-moving fronts are bringing heavy rain this weekend to Westland and Fiordland and the headwaters of the main Canterbury and Otago rivers.

MetService says a severe weather warning is in place for those areas, with the rain likely to keep falling until Monday.

On Monday parts of mid and south Canterbury, Otago and inland Southland are likely to get a period of southeasterly rain.

A further front on Tuesday is expected to bring heavy rain to northern and western areas from Nelson to Fiordland, with gale force northeast winds for a time along the South Island';s west coast.