Motorists are being urged to avoid Sydney’s CBD and public transport commuters need to consider alternative routes after a woman was killed and another stabbed by a knife-wielding man.

The alleged offender was seen acting erratically on York St about 2pm today and was detained by members of the public with a crate and wicker chairs before his arrest.

He has been taken to Day Street police station.

“A number of crime scenes have been established and a number of road closures are in place, which is believed to have significant impact on traffic and public transport this afternoon,” NSW Police said in a statement.

The state’s transport department has warned of delays to commuters from the area near King and Clarence streets, to use an alternative route and allow extra travel time.

“Motorists are advised to avoid the Sydney CBD,” the Live Traffic NSW website states, citing heavy traffic conditions.

Emergency services have remained in attendance.

The Clarence St entrance to Wynyard station was closed due to the police operation but reopened about 5pm.

Two of four northbound lanes remained closed on Clarence St at 5.30pm.

Train commuters can also enter via Wynyard Walk or York and Carrington streets.

Trains are still operating via Wynyard station although services, including the T1 North Shore line, were affected by track repairs at Auburn.

A number of buses have also been diverted.