A new alert system will give Victorians up to three days' warning of conditions that could cause deadly thunderstorm asthma, the state government has pledged.

A lack of an early warning system was a key factor in the freak thunderstorm asthma outbreak last November that killed nine people in Melbourne and landed about 8500 in hospital, Health Minister Jill Hennessy said on Sunday.

As the pollen season begins, Victorians are being urged to seek medical advice if they are prone to hay fever, whether or not they have a history of asthma, to determine if they are vulnerable to the pollen-caused illness.

Ms Hennessy said the government had overhauled the emergency response system and that authorities would now be able to monitor hospital emergency department presentations in real time.