An agreement has been reached for a giant telescope to be built in Spain's Canary Islands if it can't be put atop a Hawaii mountain considered sacred by some locals.
Telescope builder TMT International Observatory says Hawaii's dorman Mauna Kea volcano remains the preferred location for the $US1.4 billion ($A1.8 billion) Thirty Metre Telescope.
But some Native Hawaiians are fighting to keep the telescope off a mountain they consider sacred.
Hawaii's Supreme Court invalidated the project's construction permit, forcing long-running hearings for a new one. It's unclear when a decision will be made.
The nonprofit TMT on Wednesday said the Canary Islands agreement was a milestone for the embattled project.
It wants to start construction next year.
The Spanish agency overseeing Canary Islands observatories says the telescope would be good for Spain and the world's astronomy community.
