A man looking at pictures of dead bodies on his phone on an early morning train sparked a security scare that shut down two platforms and caused heavy delays at Flinders Street Station.

Police Chief Commissioner Graham Ashton has told radio station 3AW that police were called after passengers noticed a man looking at pictures of bodies on the Frankston line train on Thursday morning.

Mr Ashton said passengers were on high alert after the attack on the Houses of Parliament in London overnight.

"We had a report, I think from the events last night and the hyper-vigilance in the community ... we had a report of someone who looking at deceased bodies on a mobile phone."