Today may be the first official day of summer but it also marks the start of mice catching season in Arthur's Pass.

The Canterbury township is currently being overrun by millions of the tiny vermin after a heavy drop of fruit from mountain beech trees in the area.

Department of Conservation senior ranger Chris Stewart is catching between 20 and 30 a day, in a variety of ways.

"A whole series of things from poison to different types of trap. It'll go for a little while until the beech seed is all gone basically and the mice won't have anything to feed on."

It's the worst rodent invasion the area's experienced in almost 20 years.

Stewart says the population explosion will have a domino affect as other pests eat the mice.

"That'll be in a month or two, when we'll be really trapping and putting intensively around the village to catch stoats, which have a big effect around our birds, particularly the kiwi."