Christchurch city councillors have expressed unease about fully committing to the city's new $85 million library.

The council has been asked by the project's director to underwrite the $10 million supposed to come from "philanthropic sources", which have so far failed to materialise.

Councillor Andrew Turner says that news has been sprung on the council and there's no room for it in the long term budget so the council shouldn't foot the bill.

An amendment to clarify the council's contribution is currently being drafted.