There's been intense Israeli bombardment of Gaza by air, heavier than in previous evenings, while all internet and phone communications appear to be out in the territory.
Israel has confirmed its forces are expanding their ground operations.
The internet monitoring service Netblocks posted on X, formerly known as Twitter, to say there had been a "collapse in connectivity".
The Palestinian Red Crescent says it cannot speak to its teams in Gaza.
"We are deeply concerned about the ability of our teams to continue providing their emergency medical services, especially since this disruption affects the central emergency number '101'," they wrote in a post on X.
Meanwhile sirens alerted people in southern Israel to rocket fire from Gaza.
On Friday, the Israeli military again told Gaza City citizens to move south after announcing the expansion of its military operation.
In a press conference, spokesman Daniel Hagari said the military had "increased the attacks in Gaza. The air force widely attacks underground targets and terrorist infrastructure, very significantly".
"In continuation of the offensive activity we carried out in the last few days, the ground forces are expanding the ground activity this evening."
Currently we can't get hold of people in Gaza with communications still down.
For example the OceanNewsUK tried to send a WhatsApp message at 6.40pm local (nearly three hours ago) - it still just has a single tick meaning it hasn't been received by the person's phone.
Mobile phone call attempts just get an unobtainable message.
We've had the same for several other call attempts - messages and calls aren't going through.
OceanNewsUK reporter Mehdi Musawi tried to reach journalists and health officials in Gaza all day and could only get short replies on WhatsApp. Eventually, they got through to Gaza's Al Shifa hospital, but by evening all lines of communication were down.
By then, live footage showed complete darkness across the region. The reporter sent messages to everyone he had spoken to earlier in the day - but they did not deliver.
The panic and anxiety is spreading within the Palestinian diaspora.
For the past 20 days, sporadic, limited exchanges on WhatsApp have brought occasional moments of respite.
However, any extended gap in communication has been met with paralysing anxiety - marked by questions like: "Are they dead, are they alive, was their house bombed too?"
In one WhatsApp group relatives from around the world have been frantically messaging since the blackout.
"Oh my god!!" one wrote.
"It seems a ground offensive may start," wrote another.
The near-total telecommunications blackout in Gaza risks providing cover for "mass atrocities", Human Rights Watch said.
"This information blackout risks providing cover for mass atrocities and contributing to impunity for human rights violations," the group's senior technology and human rights researcher, Deborah Brown, said in a statement.
The Palestinian telecoms provider Jawwal says there is a "complete interruption of all communication and internet services with the Gaza strip in light of the ongoing aggression," which it says has cut the "last of the international routes" connecting Gaza to the outside world.
We've asked the Israeli military to comment on the communications outage but so far they have not responded.
