Alaoui Ismaili, a local civil defence commander, said the rescue operation was slow because of the narrow streets in the old city medina district where the collapsed mosque minaret is located.
"We are using only manpower, not equipment as we cannot bring heavy equipment through these streets," he said.
"We are moving with great cautiousness also because the walls of houses and shops adjacent to the mosque are fragile especially after the heavy rains of the past days."
Khaled Rahmouni, a Meknes, whose home is near the mosque told the Reuters news agency: "About 300 worshippers gathered inside the mosque for the Friday afternoon mass prayers.
"When the imam [preacher] was about to start his sermon, the minaret went down."
The lightly injured were hospitalised in Meknes while those with serious injuries were taken to Fes, 60km north of the town, state television station said.
Angry residents accused authorities of ignoring warnings about the dilapidated state of the mosque.
"We told them many times before that there were widening cracks on the walls and that its minaret had begun tipping over but they ignored the warning," one man, who gave his name only as Mohammed, was quoted by the Reuters news agency as saying.
Mohamed and other residents said they believed the accident could have been averted if the warnings had been heeded.
King Mohammed VI sent the interior minister and religious affairs minister to Meknes, about 120km east of the capital, Rabat, to visit the injured and supervise the rescue operations.
The king also ordered the reconstruction of the minaret "keeping to its original form", the interior ministry statement said.
Neglected buildings in the old quarters of the country's cities collapse fairly often, but the fall of a minaret is rare.