Scientists say the Antarctic population could be three times bigger than it was 25 years ago.
There are also reports of some increases in northern hemisphere blue whales. But so few animals survived the harpoons that any recovery will be a very slow process.
The blue whale (Balaenoptera musculus) is the great iconic whale species; it is the largest mammal, possibly the largest animal, to ever inhabit the Earth.
The news of its gradual retreat from the brink comes from the scientific committee of the International Whaling Commission (IWC), which is holding its annual meeting here.
It suggests the number of Antarctic blue whales may have risen from about 500 animals a quarter of a century ago to around 1,500 now.
In studiedly unexcited prose, its report says: "The committee agreed that there was evidence for an increase in blue whales in some areas of the Antarctic.
"But without sufficient time to explore issues of potential bias that were raised, it was not possible to accept specific estimates of abundance and trends at this time."
Dr Justin Cooke is attending the meeting as a representative of IUCN-The World Conservation Union. He told BBC News Online: "There've been three surveys of the Antarctic since the late 1970s.
"The first team saw about five blue whales a year, but the latest saw around 15.
"It is a statistically significant signal. People have suspected the whales were increasing for some time, but this is the first year the scientific committee has thought the growth is above the borderline of detectability.
"There are still some doubts, though. It's only recently that good observational criteria have been developed for distinguishing blue whales from the closely-related pygmy blues.
"So there is a slight question mark over the identity of the animals
that have been seen - it could be the pygmies simply moving into an area
vacated by the true blues."
In 1929-30, the whalers' most successful season, they managed
to kill 30,000 Antarctic blue whales.
The committee says there are suggestions that blue whales may have fallen to less than 3% of their level in the 1920s by the time they were given protection in the mid-1960s.
Scientific committee sources have told BBC News Online of signs that some northern hemisphere blue whale populations are also showing signs of growth.
They say there is evidence of more blue whales around Iceland and in the Gulf of St Lawrence, off Canada's east coast.
Estimates of total numbers north of the Equator are very difficult to establish.
The committee wants more non-lethal research done to improve ways of distinguishing between very similar sub-species of whale, and says analysis of their calls and songs may be a reliable species indicator.
By Alex Kirby