More than 700 pilgrims were crushed to death on Thursday in a stampede near Saudi Arabia’s holy city of Mecca that also injured almost 900 others — the deadliest tragedy to mar the hajj pilgrimage in more than 20 years.

The disaster began when two waves of pilgrims converged on the way to performing the “stoning the devil” ritual, in which they throw pebbles against three columns at Jamarat, witnesses and Saudi officials said.

“I saw someone trip over someone in a wheelchair and several people tripping over him. People were climbing over one another just to breathe,” said Abdullah Lotfy, 44, of Egypt. “It was like a wave. You go forward and suddenly you go back.”

The tragedy claimed at least 717 lives and left 863 wounded in Mina, a neighborhood about three miles from Mecca with more than 160,000 tents.

“There was no preparation. What happened was more than they were ready for,” Lotfy said, raising questions about the kingdom’s ability to handle about 2 million people on the five-day pilgrimage.

Two weeks ago, at least 111 people were killed and more than 390 injured when a crane collapsed at the Grand Mosque in Mecca during high winds.

At least 95 Iranians died and about 150 were injured in Thursday’s calamity.

Said Ohadi, head of the Iranian hajj organizing agency, accused Saudi officials of mismanagement and cited “safety errors.”

“Saudi officials should be held accountable,” he said.

But a Saudi official blamed the pilgrims.

“Many pilgrims move without respecting the timetables” set for the hajj, Health Minister Khaled al-Falih said. “If the pilgrims had followed instructions, this type of accident could have been avoided.”

Saudi Crown Prince Mohammed bin Nayef ordered an investigation.

Previous hajj stampedes claimed more than 360 lives in 2006 and 244 in 2004. In the deadliest hajj catastrophe, 1,426 pilgrims died in a stampede in a tunnel in Mina in 1990.