Hague said European countries could switch from using Russian gas to supplies from the United States or elsewhere in protest at Moscow's actions.
He told BBC TV that a referendum in Crimea about whether to leave Ukraine scheduled for March 16 would come "ridiculously quick".
"The world will not be able to regard that as a free or fair referendum," Hague said.
He dismissed suggestions that Moscow was oblivious to the West's anger at its actions in Crimea.
Hague said that unless a diplomatic solution could be found, "there would be far-reaching trade and economic consequences".
Possible measures such as visa freezes and travel bans would "be taken very seriously by the individuals concerned".
"Those are things over time which I think will mean this (the intervention in Ukraine) has been a serious miscalculation."
Although there have been no armed clashes yet, Hague warned that a lack of progress through negotiations would "bring the real danger of a real shooting conflict".
