A state government minister has been infected with Covid-19 and another minister is in isolation as a cluster in the Australian city of Sydney worsens.

New South Wales agriculture minister Adam Marshall said he was told on Thursday that he had tested positive after dining with three government colleagues on Monday at a Sydney restaurant, where a diner was infected.

All four legislators had been attending parliament as recently as Tuesday.

Health minister Brad Hazard said he was self-isolating after being exposed to a potential case at Parliament House.

Mr Hazzard said while standing next to premier Gladys Berejiklian at daily pandemic media briefings that he thought she was “fairly safe”.

Pandemic restrictions tightened in Sydney on Thursday as a cluster of the Delta variant increased and states banned travel from either parts of Sydney or from anywhere in New South Wales.

The cluster began last week when a Sydney airport limousine driver tested positive.

He was not vaccinated and is suspected to have been infected while transporting a foreign air crew.

The cluster had grown to 31 cases by Wednesday.