Some are alive and some are presumed dead, military spokesman Lt Col Jonathan Conricus said.

Children, women, the elderly and the disabled were among those taken, he said.

"These are numbers that were up until now unimaginable," he said. "This will shape the future of this war."

Hamas says the number of Israelis captured was "several times greater" than dozens and they had been taken to locations throughout the Gaza Strip.

Israel's Prime Minister Benjamin Netanyahu said Hamas was responsible for their wellbeing and Israel would "settle the score with anyone who harms them".

Footage shows Israelis being taken from homes
There are numerous videos circulating online purporting to show Israelis in the hands of Hamas fighters.

One video posted that has been verified by the BBC shows a truck being driven through crowds on the Gaza Strip, purportedly carrying Israeli hostages.

Another, geo-located to the Gaza Strip, shows a barefooted woman being dragged from the back of a truck with bloodied hands tied behind her back.

Couple taken at outdoor rave
Some hostages are said to have been taken from an outdoor party in Kibbutz Re'im, a suburb in the city of Ofakim in Israel's south - not far from Gaza.

Witnesses told Israeli media that attackers on motorcycles began firing at attendees, many of whom are still missing.

Videos posted on social media, which have not been verified by the BBC, appear to show one woman who attended the party being kidnapped and held on a motorcycle by two men.

The woman was identified by her partner's brother Moshe Or as an Israeli woman called Noa Argamani.

He had reported her missing before seeing her and his brother in the videos, both held by several militants.

"I saw Noa in the video scared and frightened, I can't imagine what's going through her mind at all - screaming in panic on a motorcycle," Mr Or said in an interview with Israeli broadcaster Channel 12.

A later video - also not verified by the BBC - appears to show her sipping water in a room in Gaza.

Watch: Video purportedly shows captured Israeli tank in Gaza

Hostage situations in Israeli towns

Outside the Gaza Strip, Israeli military forces have reportedly freed Israeli civilians who were being held hostage in two locations in the south.

In Kibbutz Be'eri, hostages who were being held in a dining room were rescued after 18 hours, Israel's TV channels reported.

Israeli media reports suggested that up to 50 people had been held there.

Speaking to Reuters news agency, a woman identified as Ella said she had been barricaded in a bomb shelter for hours in the town.

"We can hear a lot of gunfire, we were told that terrorists are in the dining hall, we can hear a lot of shooting," she said.

"I've lost contact with my family. I know my father has been kidnapped... no one is telling us what's going on. I don't know if my mother is alive."

A video verified by the BBC shows people being led along a street without shoes on by militants in Be'eri. It is unclear if these people were the same hostages as those held in the dining hall.

Meanwhile, in Kibbutz Urim, a suburb in the city of Ofakim, two Israelis were rescued after being taken hostage by Hamas militants in a house for hours on Saturday, according to Israel's public broadcaster Kan.

Gunmen had entered the city and opened fire on residents as they fled to bomb shelters after rocket alarms were set off in the city,Israeli media reported.

The two residents had stayed in their apartment, where four militants then took them hostage. The militants were later killed by Israeli forces.

Three Israeli soldiers were moderately and lightly wounded during the rescue, Kan said.

By Alys Davies