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.
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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.
