Here are some accounts from people at the pilgrimage, including BBC journalists who witnessed the crush.
"Where I'm standing, here in the centre of Mina city, I can see dead bodies wrapped in white cloth. Police have barricaded the area so I couldn't count them, but dead bodies stretch as far as my eyes can see.
"Surrounding the area some relatives are hanging around in mourning and other pilgrims who are in the tent city in Mina are also coming round to see the bodies and also to sympathise and mourn. Police officials are stopping people from passing through the area while they deal with all the dead bodies, while ambulances are moving in and out.
"Because of the lack of access, we don't know what the ambulances are doing. Helicopters are hovering over the area where the bodies are being kept."
"My group and I went there very early in the morning because we knew it would be too crowded.
"After the throwing-the-stone ritual we walked back to our tent. It was already packed, difficult to move and also difficult to breath. People were everywhere, forcefully trying to get their way further.
"People were starting to fall. I saw an Indonesian being cared for by paramedics. More people fell, or lay down, I thought because they were caught by heat, I'm not sure. Thanks to God, we managed to get to our tent at about 9am. Much later I heard about the stampede. It is horrible. The news left me in shock."
"I was in the crowd and most people, I would say 90%, are very peaceful. Then you get the young people and the heat is quite unrelenting as well. People want to do it quickly, they want to finish and, because it would get hot, people were pushing.
"I can't believe what happened. It's tragic. At the end of the day [we have to] put up our hands and ask Allah for mercy."
"I was at the centre of the stampede," Mr Bamidele told the Vanguard newspaper. "Saudi police and traffic officials who used to control movement were not available. In fact it was after the stampede that they arrived. I managed to escape unhurt."
"There was crowding. The police had closed all entrances and exits to the pilgrims' camp, leaving only one.
"I saw dead bodies in front of me and injuries and suffocation. We removed the victims with the police. They [the police] don't even know the roads and the places around here."
"People were going towards the direction of throwing the stones while others were coming in the opposite direction. Then it became chaotic and suddenly people started going down. There were people from Nigeria, Niger, Chad and Senegal among other nationalities. People were just climbing on top of others in order to move to a safer place and that's how some people died.
"People were chanting Allah's name while others were crying, including children and infants. People fell on the ground seeking help but there was no-one to give them a helping hand.
"Everybody seemed to be on their own. It affected some members of our group. I lost my aunt as a result of the stampede and at the moment, two women from our entourage - a mother and her daughter - are still missing."
"A witness who escaped the stampede said that what actually happened was that the Saudi security at the scene blocked one of the roads to the Jamarat (stoning the devil).
"This happened as thousands of pilgrims from different countries like Iran, Cameroon, Ghana and Niger were going to the Jamarat. Therefore, as those who finished stoning the devil were coming back on the same route, they met those heading to the place.
"There was a kind of collision between the two groups moving in opposite directions on the same road. Those in the middle were the most affected."
"Last night, I was coming back from Muzdalifa to Jamarat with my family on the train. We were at the station before anyone else and the train was delayed. This led to a huge number of people gathered at the station. Finally when the train arrived at 02:00, there was chaos as tired pilgrims tried to board.
"During the journey, the train stopped in the middle of nowhere for about half an hour. People were getting agitated and some even tried to open the emergency gate as we were all suffocating due to the heat and exhaustion. Finally we reached Jamarat and after performing the stone-throwing we left, only to find out that a few hours later this sad incident had occurred.
"I discovered the reason for the delayed train was that the Saudi king was performing Hajj and they did not want anyone to enter Mecca. They stopped the trains and blocked the roads. And when he finished, everyone tried to get in at once."
"The organisation by the Saudi authorities has been fantastic. We cannot blame them. There are many safety precautions in place. I have been to Mecca to carry out the Hajj a number of times over the past 20 years. This time I am here with my wife, son, daughter-in-law and mother-in-law.
"From what I have seen on the ground, for the past 10 days there is great organisation by the Saudi authorities. We cannot blame them...
"I saw a man faint in the heat and of exhaustion and 10 medical staff ran to his aid. On every escalator there are people to help those on and off. The safety precautions are more than adequate. I would go as far as to say they are over-the-top."
A stampede during the annual Hajj pilgrimage in Saudi Arabia has killed at least 700 people and injured more than 860.