A powerful 7.4-magnitude earthquake has rocked much of New Zealand's South Island. No immediate tsunami alert has been issued and no injuries have been reported.

The quake, which hit 19 miles (30 kilometers) west of the southern city of Christchurch, shook a wide area with initial radio reports saying items were tossed from store shelves and roof tiles cracked by the strong temblor.

Geological agency GNS Science says the earthquake was 21 miles (33 kilometers) below the earth's surface.

New Zealand's National Radio reports the temblor hit at 4:35 a.m. shaking thousands of residents awake. There are no immediate reports of serious damage.