Net migration from outside the European Union is unlikely to fall significantly without new Government action, according to a campaign group.
Migration Watch UK calculated that the balance between arrivals and departures from non-EU countries could run at around 155,000 a year until 2021.
This would mean net long-term migration would be running above ministers' target of less than 100,000, without taking account of arrivals from Europe.
The latest official figures show long-term non-EU net migration was estimated at 175,000 last year.
Migration Watch UK, which campaigns for tighter immigration controls, examined a series of data sources to estimate the future level.
Its analysis concluded that non-EU net migration "could well stand at around 155,000 for the next five years".
Lord Green of Deddington, chairman of Migration Watch UK, said "unless determined action is taken, it is extremely unlikely that non-EU migration will fall significantly in the next five years".
He added: "This should be a wake-up call for the Government to take further action if overall net migration, after subtracting British emigration, is to be brought down to sustainable levels.
"Brexit should help considerably but further action on non-EU migration is essential."
Whereas EU citizens can come to Britain under free movement rules, immigration from outside the bloc is subject to restrictions, with non-EU nationals requiring a visa to work, study or join family in the country.
Since the referendum vote, focus has fallen on how the regime governing EU migration will change after Brexit.
A Home Office spokesman said: "We remain committed to bringing net migration levels down to sustainable levels.
"Non-EU citizens make a vital contribution to the UK economy and our society, but the UK needs a fair and controlled immigration policy and that is exactly what this Government will deliver.
"We have already taken action to restrict non-EU migration, including increasing the minimum salary threshold for skilled workers and introducing measures to ensure family migration doesn't put an unacceptable burden on taxpayers."
Overall international net long-term migration was estimated to be 248,000 last year, down 84,000 compared with the previous year. The latest batch of figures will be published on Thursday.