A "high-value burglary" has taken place at a jewellery shop in central Milton Keynes, police say.
Thieves broke into Fraser Hart, in Silbury Arcade, about 03:30 GMT and caused "extensive damage" to the shop and surrounding area.
The burglars tried to cover their escape by starting a fire nearby and padlocking a chain across the road to prevent a police pursuit.
Access to parts of the shopping centre has been restricted for investigations.
It appears that tree trunks were also deliberately placed across Marlborough Gate, which runs alongside the shopping centre, causing roads around the Centre:MK to be closed for some time.
Det Ch Insp Kelly Glister, of Thames Valley Police, said: "It is fortunate that nobody was hurt during this incident.
"This was a deliberate and well-planned [crime] which would have meant the offenders would have been in the area beforehand as part of their preparations."