The number of people still "uncontactable" in the wake of former Cyclone Gabrielle lashing New Zealand two weeks ago has dropped to 23, police say. 

Authorities have been working to reach people who friends or family had registered as uncontactable.

The number of people uncontactable reached 6,000 immediately after the former cyclone hit due to communications to many areas being cut off.

"Getting in touch with those remaining 23 remains a priority for police and we are working as fast as we can, using a number of different methods," New Zealand police said in its statement.

Police said the situation in the Gisborne region was constantly changing, going from no internet connection to fully operational.

"Staff are making sure the wi-fi connections are not only available for police, but also for our communities as people congregate in those areas to reconnect with their families and friends," police said.

The weather system caused widespread havoc across New Zealand's North Island when it hit, leaving at least 11 people dead and displacing thousands.

Heavy rain is still hitting parts of Hawke's Bay, which was one of the worst-hit areas, with an emergency management group ordering the evacuation of people in the vicinity of a river in the region.

The wild weather also triggered flash floods and evacuation warnings in and around Auckland.

According to local media reports, people have been rescued from cars after becoming stranded by rising water.