Two people are in critical condition, and four others are injured when the minibus they were in rolled over 100 metres.
The crash was carrying guests to a wedding in the Hunter Valley. The crash occurred on Mount View Road at Mount View, near Cessnock, around 10:30 a.m.
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Emergency services – including paramedics, rescue crews and CareFlight helicopters -responded promptly. It took about 45 minutes to free a trapped passenger, a man in his 60s, who suffered head injuries and was airlifted to John Hunter Hospital in critical condition.
A man in his 50s suffered limb injuries and was also flown to hospital in serious condition.
Four other passengers were transported by road and are now stable.
Authorities have declared the site a crime scene.
Mount View Road is expected to remain closed for some time, and motorists are urged to avoid the area.