A second deployment of New Zealand firefighters leaves for Tasmania today to help fight bushfires.

The group of 43 will take over from two other groups, who'll return to New Zealand on Tuesday.

National Rural Fire Officer Kevin O'Connor said Tasmania currently has around 70 fires, and half of them aren't contained.

"The fires started in early January, many of them with a big lightening storm and some of them are getting bigger. The number of fires has reduced a little bit, but it's reduced because some of the fires have connected."

Kevin O'Connor said it's even though the number of fires is coming down, the area burning is getting bigger.

He said they'll be working in demanding conditions.

"There's been little or no rain for quite a period of time and it's not only hot and dry but they're working in quite steep and reasonably high altitude condition as well."

O'Connor said despite the teams being fit and managing well, it's still arduous work.