At least 29 women and children have died in a stampede after a religious gathering in the southern Pakistani city of Karachi.
An emergency was declared at Karachi's main hospitals
More than 70 are believed to have been injured, some critically, and doctors are urgently appealing for blood.
The stampede started when a girl fell down during women-only prayers in an Islamic centre.
At least 10,000 women were at the centre to mark the Prophet Muhammad's birthday, which falls on Tuesday.
The dead and injured have been taken to two different hospitals.
It is one of the worst accidents at a women's gathering in the country in many years, the BBC's Zaffar Abbas reports.
'Wave of people'
Eyewitnesses say prayers were under way when a girl tripped from the building's staircase.
Some women moved swiftly to try to save her and a terrible push-and-pull resulted in the crowd.
As people started to run out of the building, several women and children fell to the ground and were crushed under the feet of hundreds of people.
Many more died due to suffocation.
"I heard a girl crying for help and a woman stopped to pick her up," one injured woman, who identified herself as Zaibunisa, told the Associated Press news agency.
"When the woman stopped there was a wave of people who stepped over us.
"Someone pulled me to the side and after I gained consciousness, I was in the hospital."
An emergency has been declared at the city's two main hospitals and appeals are being made through local radio stations for blood.
Did you witness, or were you affected by, the Karachi tragedy? Send us your comments using the form below.
This is a very tragic incident. We have never before seen such a type of accident in this city which has involved women and children. The management should immediately look into the matter and take permanent steps to avoid such incidents in the future and take to task those who are responsible.
Pervez Ahmed, Riyadh, Saudi Arabia
Karachi is my city. I find myself broken by the tragedy.
Zehra, Ankara, Turkey
It must have been very painful and I feel sorry for those who died.
My heart goes out to the families and individuals who lost their loved ones as a consequence of this tragic incident.
Aadil Anvery, Raleigh, North Carolina, USA
I am shocked at this terrible news and my prayers are with the people who are affected by this terrible disaster. I feel sorry for those who died.
bilal kazim khan, london united kingdom
My most sincere condolonces are sent to the victims of this tragedy.
M. Dagher, Plympton, Massachusetts, USA
It is a very tragic incident .. we must not lose patience and feel insecure during such big gatherings ... We must improve our discipline during these religious gatherings .... no doubt it has left all Pakistanis around the globe grieved ...
A tragic accident during such a precious time. This country has witnessed enough turmoil to last a lifetime.
Seems like the authorities have not learned a lesson from the frequent stampedes that happen at the Haj in Mecca. What a shame to have so many innocent lives lost. May God bless those souls.
Alex Gomez, Victoria, CANADA.
By nature, we South-Asians tend to panic quickly, especially the women. We need to be more calm, more level-minded and more in-charge. A positive, systematic approach helping hand is always better than a random, chaotic army of helpers.
Shabbir Mandviwala, Houston, Texas
The blame is on the authourities for allowing such immense over-crowding, the local government and police must be held accountable otherwise such incidents will never stop in Pakistan
Ghazan Khan, London
This should be investigated ASAP and fully; the mosque management, the design, the bylaws of number of people allowed inside this building, etc. Karachi MUST not hide the facts....very tragic indeed! Our prayers are with ALL involved.
Homi, Delta, Canada
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