The Denver Post made the call at approximately 9:15 p.m.
Amendment 64 led with 52.7 percent voting yes and 47.3 percent voting no, with 1,507,746 votes or more than 50 percent of active voters counted, according to the Colorado Secretary of State's office. The office said 25 counties had reported.
The early results prompted cheers throughout Casselman's, a downtown Denver bar where hundreds of supporters were gathering.
Mason Tvert, co-director of Yes on 64, said the crowd was cautiously optimistic.
"We're not going to jump to any conclusions just yet," he said. "But we believe Colorado voters have decided to take a more sensible approach to how we deal with marijuana in the state."
If the amendment passes, Colorado could become the first state to legalize recreational use of the drug, possibly clearing the way for creation of a marijuana industry. There are similar measures before voters in Washington and Oregon.
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