A 35-year-old Sri Lankan man died suddenly just hours after arriving at Christmas Island's asylum seeker processing centre on Wednesday night.

The Department of Immigration and Citizenship said the man had been transferred to the island on Wednesday and was taken to the Phosphate Hill processing centre. He was transferred to the Christmas Island Public Hospital after telling staff he was unwell, but died soon after.

North West Detention Centre on Christmas Island. Credit:James Brickwood

A DIAC spokeswoman said: ''It appears the man died of natural causes after having a cardiac arrest.''

Earlier, a spokesman said the matter had been refered to the Australian Federal Police, and the department would co-operate with any investigation.