NSW is losing residents at the fastest rate in a decade, with an exodus to Victoria set to make Melbourne the country's most populous city by the 2030s.

The figures come amid calls from NSW Premier Gladys Berejiklian to slash the state's migrant intake in half and raises questions about the state's ability to hold onto its residents while still attracting new ones.

Victoria, which is growing at the fastest rate in the country, has urged more migrants to fill up a state that has lagged its northern neighbour since federation, hurling the east coast into another decade of economic competition over jobs, infrastructure and house prices.

Daniel Andrews and Gladys Berejiklian. Credit:AAP

More than 5000 residents left NSW in the three months to June, with 21,000 leaving in 2017-18 – the fastest rate since 2008. Most of them went to Victoria, which added 14,000 people.