'I'm okay mum': Young hostage contacts his mother from inside Sydney café

Sydney radio broadcaster Ray Hadley has spoken with a woman who says she is the mother of a young hostage caught up in the Lindt Café siege.

The 18-year-old apprentice plumber texted his mother, identified by her first name "Mel", this afternoon to let her know he is still okay.

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"It was just too surreal, I couldn't believe it," she said.

The young man was on a job in the city when he dropped into the café to grab a coffee.

"He said 'Mum, I'm in the Lindt Café in Sydney' and my heart just dropped.

"I sent back a text message and said 'what's going on, are you okay?' and he just sent back a message saying 'I'm okay Mum, can't talk' and left it at that and I haven't heard anything since then."