GIANT snow mazes, illuminated frozen towers and crystal palaces etched from vast blocks of ice greeted visitors to China's annual ice festival in Harbin.

The frozen dreamscapes have drawn millions of visitors over the years to the wintery northeastern city, which opened the festival on Tuesday despite small Covid-19 outbreaks across China.

Preparations for the annual winter celebration begin weeks in advance, with workers mining millions of cubic feet of ice from the surface of the Songhua river over long, gruelling shifts.

Walls of ice carved into the shape of a giant flower were lit up on Tuesday night as the festival opened.

The 2022 Beijing Winter Games have inspired a push across China to promote winter sports and tourism, with the number of Chinese snow resorts increasing nearly fourfold in the past decade.

China has largely brought coronavirus infections under control domestically, with entertainment and cultural venues reopening and life largely returning to normal in recent months.

But small outbreaks in multiple cities have prompted authorities to step up testing and travel restrictions.

Visitors to this year's festival are required to show a "health code" on a contact-tracing app and have their temperatures measured before entering venues.