Labor Lyons MHA Rebecca White yesterday promised to contribute $11.5 million to construct the new building.

Ms White said the St Helens District Hospital was vital for the East Coast.

"It serves some 4000 people year round but that swells to more than 10,000 during holiday periods. For a region that can often be cut off by floods, it's important we get our health services right," Ms White said.

The existing hospital is almost 40 years old and was built on a site prone to flooding.

"The hospital had to be evacuated due to flooding three times in a period of 18months, most recently in May 2012," Ms White said.

The announcement follows the signing of a memorandum of understanding by the Break O'Day Council, the Department of Health and Human Services and Tasmanian Health Organisation North to address the issue.

Last year, the council bought a block of land it believes is suitable for the new hospital.

Ms White said the new building would improve patient comfort and privacy, have more space for visiting medical services and better storage and kitchen facilities.

Meanwhile, the Greens and Liberals unveiled their mental health policies.

Establishing a new independent statutory body to be known as the Mental Health Commission and creating a new position of chief health economist to provide advice to government on healthcare were the key planks of the Greens' $3.75 million plan.

"This is about removing pork barrelling from decisions over funding, and ensuring governments take a long-term and big-picture view of health issues, including mental health," Greens leader Nick McKim said.

The Liberals have committed almost $2 million to make it easier for users to navigate the mental health system.

Liberal health spokesman Jeremy Rockliff said an overhaul was needed to make it "seamless and integrated" from the start to finish of a patient's care.

"Tasmania's mental health system has become complex, disjointed and confusing to navigate," Mr Rockliff said.

The Mental Health Council of Tasmania has 18 months to analyse the system and identify gaps and make recommendations for reform.

The commitment is on top of $3 million already promised for suicide prevention.

Rural Alive and Well will also receives a $1 million boost to continue its support services to people struggling in regional Tasmania and $300,000 will be invested in mental health outreach services provided by the Neighbourhood House network.