An advocate for asylum seekers on Nauru says twenty-three refugees transferred from Australia's Christmas Island to Nauru have joined the hunger strike.
Nearly 400 men are housed at the detention centre on the island.
Ian Rintoul of the Australian Refugee Action Coalition says yesterday was the 12th day of the mass hunger strike.
He says on Monday 12 people required treatment at the medical centre, and Sunday it was 15.
He says there are also growing fears for the welfare of the Iranian man in the 32nd day of his hunger strike.
Doctors have told the man he will be transferred to the Nauru hospital in the next few days, and warned he faces kidney failure and increased risk of a hear attack if the hunger strike continues.
Ian Rintoul says the possibility of the Nauruan hunger strikers suffering permanent damage grows day by day.
He says there were also further signs of stress on the medical centre after local police were called when one of the hunger strikers staged a two-hour naked protest after doctors had refused for a week to get painkillers for a toothache.
Mr Rintoul says it's is increasingly urgent the Australian Immigration Minister intervenes.