The armed robber at the Carlton Hotel in Cannes targeted a temporary jewellery exhibition it was hosting from a diamond house owned by Israeli billionaire Lev Leviev.
It remains unclear how many pieces were stolen.
The valuable jewels were due to be on public display until the end of August.
More top news
Doctors cannot explain it but the extraordinary bond between new mum Holli Cheung and her son Jordan may have saved her life.
David Cameron has begun a whirlwind tour of Europe to discuss his terms for renegotiating the UK's membership of the EU with key leaders.
Through the rest of today showers will continue across many northern areas, whereas for much of England and Wales it'll stay largely dry.