Euthanasia advocate Philip Nitschke has accused Customs officials of accessing hundreds of patients' sensitive records on his laptop after detaining him at Melbourne Airport on Tuesday morning.

Speaking from a plane about to fly to Los Angeles, Dr Nitschke said he had only just made his flight after he and his wife were kept by custom and immigration officials for 45 minutes.

Euthanasia campaigner Philip Nitschke. Credit:Ryan Osland

Dr Nitschke, the founder and director of right-to-die group Exit International, said his laptop and mobile phone were taken from him after he was stopped about 10.30am.

He said he was told he had been picked out at random to see if he was leaving Australia with excess cash and that his devices were taken to confirm his phone was not stolen.