WELLINGTON (Reuters) - New Zealand on Thursday formally closed to visitors the sub-Antarctic Auckland and Campbell Islands, fearing humans may be at risk from a mysterious illness that has killed thousands of rare sea lion pups. Conservation Minister Nick Smith said the islands, which were due to be visited by one domestic and two international tourist boats this month, would remain closed until the situation had returned to normal. In the last week, many hundreds of Hooker sea lion pups have

been found dead on and around the islands, which are breeding grounds for the threatened species. Scientific tests have so far failed to establish what has caused the mass fatalities. No humans are known to have contracted the illness, but Smith said it was wise to be cautious. If the cause of death was bacterial, rather than a virus or

biotoxin, there could be a risk to humans. Until there was more information, non-essential people would be restricted from landing. This would also reduce the risk of spreading any disease. A Department of Conservation (DOC) veterinarian discovered the dead mammals eight days ago on the remote islands, about 400 km (240 miles) south of New Zealand's South Island. More than 1,200 dead animals have been found and all appear outwardly healthy and in good condition. Establishing the cause of death could take up to three weeks, DOC said. Smith said the sea lions, with a population of between 11,000 and 15,000, were the most endangered in the world.