Some Indian experts have warned that the explosion at Japan's Fukushima Daiichi nuclear complex may be worst than Chernobyl even as the quake-hit nation seeks to reassure its people that the country would not experience a full- blown nuclear disaster.

At least 15 people have been reportedly admitted to hospital with symptoms of radiation poisoning after a blast ripped through a reactor at the Fukushima nuclear power plant yesterday. The emergency cooling system is said to have been failed at another reactor at the Fukushima plant.

The authorities, who have ordered the evacuation of 170,000 people from the area within a radius of 20 km at Fukushima, 250 km northeast of capital Tokyo, however, said there are no health concerns though fluctuations in the radiation level can be expected.

But some Indian experts are not convinced.

"There are a total of 10 reactors at the two plants at Fukushima nuclear complex. Yesterday, there was an explosion at the No. 1 nuclear plant in the wake of 8.9 magnitude quake and tsunami in the region, which destroyed a reactor and reports suggest that another reactor may also explode," said Delhi-based nuke security expert V.K. Duggal.

"The Japanese government hasn't yet provided accurate information regarding threat posed by explosions. This is very worrying. The disaster may turn out to be more dangerous than Chernobyl -- both from the standpoint of population's exposure to radioactive material and radioactive contamination in the area," said Duggal.

Another expert Professor Subodh Gupta agreed. "We aren't at all aware of the status of the fuel in the core of the reactor that exploded yesterday at the nuclear complex. We don't know whether the core is uncovered, if the fuel is breaking up or melting. This is dangerous," he said.

Japan's nuclear safety agency has rated the incident at four on the international scale of zero to seven. The country's US envoy Ichiro Fujisaki told CNN "there was a partial melt of a fuel rod... but it's nothing like a whole reactor melting."

"But the explosion must have caused radioactive materials and gases to emit into the air. The most vulnerable elements discharged were iodine and cesium, two by-products of the nuclear fission process. These volatile compounds can well spread into the atmosphere and cause a massive disaster," said Professor Divya Mishra of Mumbai University.

Health officials in Japan said they will distribute iodine tablets as a precaution as iodine protects against radiation- induced cancer.

"The disaster could be on the scale of Chernobyl where the reactor core melted and radioactive fallout were discharged into the air, harming civilians living at a relatively great distance from the reactor. It's high time that Japan comes out with a correct assessment of the situation," said Professor Gupta.