The latest instalment of the Sydney Metro will no longer open this weekend as planned as the government waits for the national rail safety regulator to give its final approvals.

The Chatswood to Sydenham line had a target opening day of Sunday August 4, but has failed to receive the necessary approvals from the Office of the National Rail Safety Regulator (ONRSR).

Transport Minister Jo Haylen today said passengers would only be waiting a little longer to jump onboard, but she was disappointed about the delay.

"This railway is 99 per cent ready," she said.

Four additional exercises need to be undertaken in partnership with Fire and Rescue NSW, before the safety regulator can give its "tick of approval".

Ms Haylen acknowledged a fire on the North West line two weeks ago — where passengers were stuck on a carriage — was one factor causing the delay, as was industrial action.

But after more than 11,000 hours of testing, Ms Haylen said she was not concerned about the network's capability.

"The railway is safe, it's not a question of safety," she said.

A new date for the opening has not been set.

Premier Chris Minns yesterday insisted the opening was on track but acknowledged the paperwork was yet to be finalised.

But the rail safety regulator said several critical safety checks were yet to be completed.

Trial runs and testing of the new line have been underway for several months and the fencing around some new stations was pulled down on Monday morning.

However, the Office of the National Rail Safety Regulator (ONRSR) said the metro was yet to be given the tick of approval.

The ONRSR said it was assessing the application as quickly as possible but could not provide an estimate on how long approvals usually take.

New bus services will be added in the North West area this weekend that will assist people travelling from Chatswood to the city.