South Korea said Tuesday it was expanding a major bird flu cull to try and contain a damaging outbreak that has continued to spread during an all-consuming political crisis.

Since the first case of the highly pathogenic H5N6 virus was confirmed in mid-November, another 43 cases have been reported and close to 10 million chickens and ducks have already been slaughtered in farms across the country.

In a statement, the agriculture ministry announced plans to cull an additional 2.5 million birds, making it the worst bird flu outbreak since 2014 when nearly 14 million were slaughtered.

The announcement came a day after health authorities issued a second nationwide "standstill" order -- effectively restricting workers at poultry farms from moving around the country for 48 hours in an effort to stop the virus from spreading.

There have been no cases of human infections from H5N6 in South Korea, although the virus killed six people in China between 2014 and April 2016.

The World Health Organisation warned earlier this year that the strain has caused "severe infection" in humans.

The current outbreak has coincided with a deepening political crisis that saw the impeachment last week of President Park Geun-Hye and has paralysed her administration.