Blenheim residents were woken at 3.30am to a loud, grinding metal sound and the ground vibrating.
Seymour St resident Jan Head said the noise got louder and louder from 3.30am on.
''It was really, really noisy,'' she said.
''It sounded like stones being ground against metal. We could feel the ground vibrating.''
She rang noise control at 3.30am then before she left for work about 5am, but the noise continued.
Marlborough District Council operations and maintenance engineer Steve Rooney said work was being done on the new civic theatre site next to Clubs of Marlborough on Alfred St.
A large water main was being re-located as part of the construction of the theatre, he said.
A new water main was being relaid in the road and under the bridge. The ends were then connected to convey water through the Blenheim business district.
The work had to be done during the night so the businesses would not be without water during the day, Mr Rooney said.
The loud noise heard by Mrs Head at 3.30am was when construction workers encountered a large, unexpected block of concrete, he said.
Workers had to break the concrete away with a jack hammer so they could continue laying the water pipes.
''It wasn't expected, but they had to get on with it,'' he said.
Work was completed about 6am.
- The Marlborough Express