Almost 6,300 firefighters are on standby in Portugal as the country gears up for the annual wildfire season amid controversy over whether enough has been done to prevent a repeat of last year's unprecedented 106 deaths.

The government says that as from Tuesday, 13 water-dropping helicopters are available, with other aircraft already contracted for the critical period from June 1.

Authorities have enacted a series of measures since last year's deadly blazes, including a national and mandatory forest cleaning program.

A severe drought last year left forests tinder-dry. Experts have blamed the large-scale wildfires on woodland that is often neglected. Rural areas of Portugal are commonly populated by elderly people who sometimes are unable to clear forest debris.

Critics say the government has been slow to act.