An alleged crayfish thief has been charged after he was spotted waving a live crustacean through Melbourne's CBD, police said.

The 26-year-old from Tasmania allegedly took the crayfish from a tank inside a restaurant in Chinatown about 1:00am (AEDT) on Saturday.

It is understood the restaurant was the West Lake yum cha eatery.

Officers patrolling the area spotted a group walking along Little Bourke Street and noticed one of them waving a live crayfish in the air.

Police arrested the man and the crustacean was returned to its tank at the restaurant.

The man was charged with theft and animal cruelty.

He was bailed to appear in the Melbourne Magistrates Court in May.