>>> overseas tonight, happening again in egypt. the last time there was violent like this, the last time tahrir square was this full of people, protesters, they were overthrowing hosni mubarak . the same thing may happen to the first democratically elected president, mohamed morsi. good evening.

>> reporter: good evening, brian. thousands of people have gathered in tahrir square. a celebration, people pointing lasers at buildings, music blaring. they feel their struggle is finally paying off, even with a little help from the country's powerful military. military helicopters trailing egyptian flags today, flying in formation above tahrir square, as the huge crowd erupted in cheers. finally, they believed the military had taken a side, their side, in the battle with mohamed morsi. the military called the protesters great, glorious and nobile, and gave morsi an ultimatum. had 48 hours to "meet the people's at t people's demands," or they will intervene.

>> morsi, i'm telling you, you have to leave, you have to leave.

>> reporter: on sunday, one year after morsi took office, millions of egyptians took to the streets in protest. there was violence, at least 16 dead, hundreds injured. muslim brotherhood headquarters was sacked. a petition calling for morsi's resignation gathered millions of signatures. a crumbling economy, basic services almost nonexistent. food and fuel often out of reach. morsi's opponents say he hijacked the revolution that outsted mubarak and imposed an islamic government that refuses to share powers. supportersay msi w elected fair and square and the military is attempting a coup and they are ready to fight. morsi is holding emergency meetings tonight. the crowd now believe his days in office are numbered. military says this is not a coup, that ending the conflict is a matter of national security . but the ultimatum, music so the ears of the protesters who toppled one leader here and bhooef they are about to do it again. tonight, the response from the u.s. has been somewhat muted, no specific reaction to what the military issued today. crowds critical of the obama administration position. they have been warming up to the muslim brotherhood over the past year.

>> eamon, above the wild scene in tahrir square, thanks.