New Brisbane trains 'too big for tunnels'

A one-centimetre construction fault has kept Brisbane's new CityTrains off the tracks.

A spokesman for Queensland Transport Minister Paul Lucas says the air conditioning units on top of the new carriages have been built 10 millimetres too big.

It has sparked concern there may not be enough clearance in the central and Roma Street tunnels.

The fault was identified during a 1,200-point check last month, with two new trains now sitting idle in Queensland Rail yards.

Queensland Rail says it is working with the manufacturer to resolve the fault before the trains are commissioned into service.

The multi-million-dollar three-car trains were due to be operational early this year.

Passenger Services general manager Michael Scanlan has asked commuters to be patient while the issues are resolved.

"We did make a public view that May we would expect these services to commence on the Gold Coast," he said.

"It's just that because it's the first of a series there's a lot more testing required.

"And what we would expect is that there's a delay on the first few units and then the manufacturer will catch up very quickly and be back on schedule quite soon."

- RADIO AUSTRALIA