Tas measles case count reaches four

Tasmanians should remain alert for measles symptoms with four cases of the infection confirmed, a senior doctor says.

Tasmanian health authorities have confirmed four cases of measles, all believed to be linked to exposure during a flight originating in Thailand.

The first case was identified at the start of May when a patient presented to Launceston General Hospital after flying from Bangkok to Melbourne and then on to Launceston on April 30, acting director of public health Mark Veitch said on Friday, confirming three subsequent adult cases.

"These secondary cases show just how contagious measles is to unvaccinated people," Dr Veitch warned, adding that all three were infected after coming in contact with the initial sufferer.