NSW Fire and Rescue workers were called to the Phillip Street courts complex, home to the Supreme and Federal Courts, around midday on Sunday to help remove water from the foyer and another three floors of the building.

It is believed the flooding started on level six, which houses Supreme Court administrative staff, and was caused by a damaged sprinkler head and a burst pipe.

The three floors below, including the Supreme Court registries on levels four and five, were also flooded. It is not yet clear when the complex will reopen.

The shutdown will affect dozens of high-profile cases, including the defamation battle between international cricketer Chris Gayle and Fairfax Media, publisher of The Sydney Morning Herald, The Age and The Canberra Times. It has been moved to the King Street court complex across the road.

"A significant flooding incident has occurred at the Law Courts complex impacting the NSW Supreme Court and Commonwealth Courts," a NSW Justice spokesperson said in a statement late on Sunday.

"Following an initial assessment the complex will be closed on Monday 30 October. Further assessment will be carried out to determine when the complex can reopen."

The spokesperson said that "in the meantime every effort is being made to relocate or re-list Supreme Court proceedings."

A spokesman for NSW Fire and Rescue told Fairfax Media late on Sunday there had been "extensive flooding" and "significant water damage" on the affected floors.

Fire and rescue workers responded to an automatic fire alarm and remained at the Law Courts complex until 4pm, when contractors arrived to continue the clean-up operation.

Apart from the shared foyer on level three, it does not appear that any floors of the Federal Court were affected by the incident.

In a statement on Sunday, the Federal Court said the building was closed on Monday "to enable investigation of any damage" and "updates will be posted on the Federal Court website on the results of that investigation."

The Supreme Court floors affected by the incident are not used as courtrooms.

In a statement, the NSW Bar Association said cases listed for Supreme Court hearings in the immediate vicinity of the Law Courts complex - the Hospital Road, King Street and St James courts - "will proceed unless members are notified otherwise".

The Darlinghurst Supreme Court is also unaffected.

Yellow and red tape marked with "Danger - No Entry " cordoned off the Law Courts complex until shortly after 7pm on Sunday. Contractors remained at the site into the evening.

The NSW Justice Department said updates would be provided on the Supreme Court website as well as over the phone from 8.30am on Monday on 1300 679 272.