The blue whale, once hunted to the verge of extinction, is making a comeback with numbers thought to have risen from a few hundred to a few thousand, scientists have said.

The International Whaling Commission's 2007 scientific report reveals that the Antarctic population of the blue whale, thought to be the largest animal ever to live on Earth, rose by 8% per year in the 25 years to 2003/04.

The report was presented to the IWC's conference in Alaska, which concluded earlier today with countries voting to continue a 21-year-old moratorium on commercial whaling.

Although difficult to accurately monitor, the number of blue whales living south of 60 degrees south is thought to have increased from 450 in the early 1980s to around 2,300, the report said.

"The most recent data is really encouraging," the IWC's head of science Greg Donovan told the BBC.

"Blue whales have now been increasing by about 7-8% per year for the last 10 years at least, for which we have good data.

"The abundance is still very low, it's about 2,300 for the whole southern hemisphere so it's a tiny fraction of what it used to be, but it's good news they're increasing."

There is less data available for the northern hemisphere, but off the Icelandic coast a recovery has also been noted.

The IWC believes the global population of blue whales, which grow to 30 metres long and weigh up to 200 tonnes, is around 4,500.

Hunters mercilessly pursued the blue whale during the 19th and 20th centuries until a ban was imposed in the 1960s, by which time the species was perilously close to extinction.

Before large-scale hunting started the global blue whale population was thought to have totalled 200,000.

With up to 30,000 killed by commercial hunters every year, the population fell to just a few hundred by the time the ban was brought in.

Scientists say the blue whale's ability to communicate with potential mates over large distances have helped stocks recover.

Meanwhile, Japan threatened to walk out of the IWC after anti-whaling countries refused to discuss a plan to allow a small amount of whaling by four Japanese coastal communities.

The anti-whaling countries also secured enough votes to continue the moratorium on hunting.

The ban, enacted in 1986, aims to protect several vulnerable species. Pro-whaling nations, including Japan, Norway and Iceland, say populations have rebounded and the ban is no longer necessary. Norway and Iceland do not recognise the ban and conduct commercial whaling.

The commission also passed Greenland's revised proposal to increase its aboriginal quota of minke whales to 200, as well as to hunt fin and bowhead whales.

Greenland originally wanted to renew hunting of humpback whales but met adamant opposition from critics who noted that humpbacks and bowheads have low reproduction cycles.