NBC's Richard Engel reports from Cairo on optimism among the young people of Egypt that fueled a successful revolution and their sense that the United States has supported their cause.
Update 1:38 p.m. ET: The White House no says President Barack Obama is expected to speak about 3 p.m. ET.
Updated 1:03 p.m. ET: The White House now says Obama's remarks will come at a "time to be determined." It previously had said Obama would speak at 1:30 p.m. ET.
Update 11:48 p.m. ET: Reuters is quoting a military source as saying Defense Minister Mohamed Hussein Tantawi is the head of the Higher Military Council that has taken control from Hosni Mubarak.
Update 11:45 a.m. ET: NBC's Richard Engel reports from Cairo that a communiqué from the military — in essence, the new interim ruler of Egypt — is expected at any moment.
Update 11:20 a.m. ET: President Barack Obama will make a televised statement at 1:30 p.m. ET, the White House says.
The president was told of Mubarak's intention to resign during a meeting and watched the announcement on television, it says.
Update 11:15 a.m. ET: As word of Mubarak’s resignation spread through Cairo’s Tahrir Square, a raucous celebration erupted among the protesters who have made his departure from power their no. 1 goal. Mohamed ElBaradei, the Nobel Peace Prize winner who returned to Egypt to join the protests, said, "This is the greatest day of my life. The country has been liberated."
Update 11:03 a.m. ET: Suleiman came out for a few seconds and announced that Mubarak is resigning and that the Supreme Military Council has been appointed to administer Egypt.
The hundreds of thousands of people in Tahrir Square immediately erupted in joyous cheers.
Update 10:29 a.m. ET: NBC News, citing U.S. and Egyptian officials, reports that the message will come from Vice President Omar Suleiman, who the officials said will try to "clarify" exactly what Mubarak's speech meant.
"Obviously, they had that opportunity last night, and it was muddled," a U.S. official said.
Amid widespread reports that President Hosni Mubarak has left Cairo for his home in the resort town of Sharm El Sheikh, Egyptians are awaiting what's being described by state television as an "urgent and important" announcement from the "presidency," NBC's Richard Engel reports from Cairo.
A White House official called Mukarak's departure for Sharm el Sheikh a "positive first step," but other officials cautioned against reading too much into it, noting that it's been essentially a second full presidential center for years.
Mubarak typically spends a good part of the year in his "rest house" in Sharm el Sheikh, often receiving official guests and convening summits and conferences there, NBC's Charlene Gubash reported from Cairo.
As for the oending announcement, the word "presidency" leaves it unclear whether that would be a message from Mubarak or from Vice President Omar Suleiman, who U.S. officials are increasingly convinced has assumed full presidential authority after Mubarak's ambiguous speech yesterday, NBC's Jim Miklaszewski reports from Washington.
In fact, it's unclear exactly what role Mubarak could play except to officially hang on to his title, a U.S. official said this morning, adding, "There are nuances to this that we still don't understand."
The German government told NBC News that it hasn't gotten any "official request from the Egyptian government for Mr. Mubarak to come to Germany," referring to widespread speculation last week that Mubarak might be headed to a health clinic in Baden-Baden.