Labor's health spokesman Ryan Park has slammed the Illawarra Shoalhaven Local Health District's decision to close the 20-bed unit at the Nowra hospital for three weeks over the holiday period.

Mr Park said this was often a time when people could feel most alone and in need of help.

"This is an appalling situation and I will be writing to NSW Health Minister Brad Hazzard demanding an explanation as to why this decision was made and seeking to have it changed," he said.

"People who are very vulnerable should not have to travel past an existing service to get the treatment they require and are entitled to.

"Unfortunately this is yet another example of smaller rural and regional hospitals not getting the resources they need to service local communities."

However the health district's mental health director Julie Carter said it was typically a period of low demand at the Shoalhaven unit.

"Demand ... decreases considerably as people tend to either delay their admission or take some time out from inpatient rehabilitation to spend time with family, friends and carers," she said.

"The district is supportive of this, where clinically appropriate, as spending time with loved ones over the Christmas period instead of in hospital has shown to have a positive impact on well-being and mental health."

Ms Carter said Shoalhaven residents requiring an inpatient admission to a sub-acute unit during the period would be accommodated in Shellharbour Hospital's mental health rehabilitation unit.

"Last year, this was needed by one person over the Christmas period," she said.

Ms Carter said the district would continue to provide acute mental health services in both the community and hospital setting throughout the Christmas and New Year period.

"The well-being and care of our mental health consumers is always our first priority," she said.

If you need support contact the 24/7 Mental Health Line on 1800 011 511; Lifeline on 13 11 14 or Beyond Blue on 1300 224 636.