Armed with a hammer at the newly-renovated building on Mount Sophia, he started smashing its gleaming glass panels and plaster board.

The bill for the damage he caused in 15 minutes: $20,000.

His actions left 15 staff members of Union, an architecture and interior design collective, shocked.

No one was hurt, but the place was littered with glass shards.

Police who arrived later took the man away for questioning.

Union moved into the renovated 80,000-sq-ft complex of buildings, formerly the premises of Trinity Theological College, on June 1.

Now the only tenant there, the architectural firm occupies the single-storey church sanctuary; other tenants, also in the artistic and creative fields, have not moved in yet.

Architectural executive Mark Teo, 31, said he heard his colleagues shouting 'Keep away from the glass!' at about 10am.

He said: 'I didn't realise the man was smashing the glass at the side of building then.'

The worker was wearing a motorcycle helmet and brandishing a hammer in his right hand.

After trashing the glass panels on the side of the building, he proceeded to its back entrance and started whacking the plaster board there, but the hammer became lodged in it and its head broke.

He went into a store room where work tools were kept and emerged with another hammer, which he used on the glass panels in the rear of the building.

Then he entered Union's office space and shouted in Hokkien that he was owed money by his ex-boss Jimmy Tan.

He moved to the glass-panelled office front and bashed a hole there, before Mr Tan's sister grabbed his right arm.

Mr Teo and another colleague then disarmed him and pinned him down. The police arrived a few minutes later.

Mr Tan said the contracted worker was hired three weeks ago to do cement work for a daily wage of $60, but was fired on Monday morning after other workers complained of his shoddy work.

Mr Tan said: 'He demanded we pay him for work on Monday, but he didn't do any work at all. It's ridiculous.'

He added that a quarrel ensued then and they got into a scuffle. The police were called in to make peace.

By noon yesterday, Union's staff members were back at work although most of their office walls were gone.