Noor Yahaya Hamzah of Christchurch said the attacker started opening fire as soon as the Friday sermon began at about 1.40pm (New Zealand time) on March 15, with the prayer hall yet to be filled.
"The main prayer hall usually fits about 400 people. I seated myself right in front of the pulpit and the sermon had just begun.
"When I heard the shots, it was the shooter aiming at the people in the rooms. The main prayer hall was at the end of the mosque and the walkway leading to it had many rooms on either side.
Noor Yahaya said after running out, he kept safe by ducking behind a car with another friend, who was injured in the shooting inside the mosque.
They hid for about 20 minutes before the Armed Offender Squad (AOS) arrived.
The AOS is part of the New Zealand police force which responds to high-risk incidents.
"My injured friend could still run. He had white creamy stuff and blood from other victims splattered on him, which was also on me when we took cover. It looked like brain matter," he said in a telephone interview.
Noor Yahaya, who lives about 6km away from the mosque, said he was a regular worshipper at the mosque.
"When the AOS arrived and secured the area, we were ordered to lie on the ground," he revealed.
He said that there were two other men injured and when the paramedics came, those who were not injured were led by the police to the street facing the mosque.
"While walking outside, I saw two dead bodies. I looked into the mosque and saw bodies piled up in the main hall.
"At the front of the mosque, there were four or five dead bodies. Two more dead bodies were on the street in front of the mosque.
"The police took our details and they led us to Hagley Park in front of the mosque. Then we were taken to the hospital by the police," said Noor Yahaya, who was still traumatised by the attack.
He said many of the people he usually prayed with at the mosque were killed with many more still missing.
He hoped that they were safe, although he is prepared to expect the worse.
Noor Yahaya posted on Facebook a picture of him standing in front of the Christchurch hospital, waiting to be picked up by his wife.
At least 49 people were killed and dozens more injured when the gunman went on a rampage at the mosque and the Linwood Islamic Centre on Linwood Avenue.
Foreign Minister Datuk Seri Saifuddin Abdullah confirmed that three Malaysians were injured in the attack on the Al Noor Mosque.
The main suspect in the mass shootings at two New Zealand mosques was charged with one count of murder on Saturday, reported Reuters.
Brenton Harrison Tarrant, a 28-year old Australian citizen, appeared in a Christchurch District Court and was remanded without a plea until his next scheduled appearance in the South Island city's High Court on April 5.
Handcuffed and wearing a white prison suit, Tarrant did not speak. His court-appointed lawyer made no application for bail or name suppression.