It looks like summer is coming for the main cast of Game of Thrones.

They are getting hefty pay rises from next season, though with no guarantee their characters will survive, according to a US report.

Expected to get more than $US500,000 an episode - a spectacular $671,000 - are Emilia Clarke (Daenerys Targaryen), Peter Dinklage (Tyrion Lannister), Kit Harington (Jon Snow), Lena Headey (Cersei Lannister) and Nikolaj Coster-Waldau (Jaime Lannister).

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According to Deadline Hollywood, the five actors netted close to $US300,000 ($402,603) an episode heading into the current season six in exchange for giving cable channel HBO an option for a seventh season.

That made them among the highest-paid actors on American cable television.

Now they are are getting substantially more for season seven next year while signing on for a possible eighth season.

But even those salary boosts "does not guarantee that all five characters will survive till the end as the show's last episodes are yet to be written."

The smash hit fantasy series based on the books by George R.R. Martin is expected to have fewer episodes in coming series - possibly seven episodes for series seven and just six for series eight.

For those whose characters do survive, the new pay rises mean the main five actors could earn $8.7 million each over these two seasons, which reflects the series' massive success around the world.

Showrunners David Benioff and D.B. Weiss have said they are "approaching the finish line" of the series, telling The Hollywood Reporter before the sixth season that they are "writing the final act" and are "looking at somewhere between 70 and 75 hours before the credits roll for the last time."

But given the series' ratings and critical success, there will be huge pressure to continue in some form.

While HBO said that it doesn't discuss contract negotiations, contracts of other cast members outside the big five are reportedly yet to be negotiated.