One Northern school is believed to have had more than 100 children sick last week and other classes have reported half the students absent.

Schools are asking sick children to stay at home to avoid spreading the flu.

However, Learning Services North general manager Laurie Andrew said the levels of absenteeism in schools was not significantly different to previous winters.

Medicare Local Tasmania media spokeswoman Dr Leanne Jones said more school children were going to doctors, and general practitioner figures collated for the past fortnight showed a spike in the number of flu cases.

However, she said there were probably many more sick people who just stayed home.

``It's really affecting young people, however it's proving the over-65s vaccination program is working,'' Dr Jones said.

``It's particularly the 20 to 40 age group - yet this is also the larger group that must present some kind of proof or certificate for being ill to their workplace.''

The two main age groups affected were the under 9s and the 35 to 44 age group.

Dr Jones said parents should keep their child home if they had flu and ensure good fluid intake.

She said if symptoms persisted they should see a doctor.

Health Department Public and Environmental Health senior medical adviser Dr Mark Veitch said flu cases across the state increased in June and had remained high into July.

He said the cases of whooping cough in the state remained high, with about 100 a month.