Seven people from the same village have been hospitalised in Indonesia with suspected bird flu, officials say.
Indonesian ministers have gone to assess the situation
The group is from Karo district in Northern Sumatra province, where seven members of one family died of the deadly H5N1 virus in May.
Their deaths sparked fears that the virus was mutating into a form which could pass easily from human to human, but experts later ruled this out.
Indonesia has seen more bird flu deaths this year than any other country.
A health ministry official, Runizar Ruesin, said experts were still waiting for test results from the group and any cluster "must be scientifically proved".
But any new cluster of bird flu sufferers would cause alarm, especially since foreign health experts say Indonesia has not managed to control the disease's spread among birds.
"There are two clusters, one with two sisters, the other with three family members, and another two of their neighbours," Health Ministry official Nyoman Kandun told The Associated Press news agency.
Chickens in the area where the suspected victims live had tested positive for the bird flu virus, another official said.
Indonesian ministers have travelled to the region to assess the situation.
Experts fear that the virus could mutate to a form which could be easily passed from human to human, triggering a pandemic and potentially putting millions of lives at risk.
Indonesia has been criticised for not taking tougher action
The World Health Organization said that limited human-to-human transmission had taken place in the case in May, but emphasised that this did not signal a major change in the spread of the disease.
Indonesia recorded its 42nd human bird flu death at the end of July, the same total as in Vietnam.
But while Vietnam has been praised for controlling the disease's spread among birds, Indonesia's government has been criticised for its reluctance to cull fowl in infected areas and for the fact that many Indonesians still do not understand the danger of living in close proximity to chickens and ducks.
Globally, more than 130 people have died of bird flu since late 2003. Most of the deaths have been in East Asia, but the virus has also spread to Europe, Africa and South and Central Asia.