TOKYO (AFP) - Japanese police are probing the deaths of 46 patients on the same floor of a hospital where a pair of elderly men were fatally poisoned, reports said on Monday (Oct 3).

An autopsy on the two men who died at the hospital in Yokohama determined they were caused by a chemical found in disinfectant, public broadcaster NHK and other media reported earlier.

Police reportedly suspect the chemical was injected into intravenous drips that were administered to the two 88-year-old victims, Sozo Nishikawa and Nobuo Yamaki. The men both died last month.

But the probe has grown with authorities looking at how almost four dozen others died at the hospital since early July, although some were already seriously ill.

Hospital staff reportedly found puncture marks in 10 intravenous bags stored near the nursing station on the same floor.

"We see many people pass away due to the nature of this hospital, but had the impression that the number of those dying was increasing a bit," a hospital official told Kyodo News.

Many have already been cremated, making determining a cause of death more difficult, reports said.

Neither police nor the hospital would confirm the news reports, and no suspects have been named.

The investigation comes two months after the murder of 19 people at a centre for the mentally disabled, Japan's worst killing spree in decades.

In 2000 a male nurse was charged with killing one patient and attempting to murder four others by poisoning them at a clinic in the northern Japanese city of Sendai.