NEW YORK (CNN) -- New York suspended all construction crane activity in the city Friday after a crane collapse on the Upper East Side killed two construction workers.



Crane wreckage lies on Manhattan's Upper East Side on Friday in a photo by iReporter Michael Schuman.



Acting Buildings Commissioner Robert LiMandri announced the suspension, in effect until Monday, and unveiled a $4 million plan to assess high-risk construction activities, including crane operations, and make recommendations to improve safety.



"This year we have seen an increase in accidents and injuries related to high-risk construction activities," LiMandri said. "We must make sure that as construction activity in the city continues to increase, the department's ability to hold the construction industry to higher safety standards keeps pace."



Friday's accident was the second deadly crane collapse in the city in less than three months. Seven people were killed and 24 were injured in March when a construction crane toppled, plowing through several residential buildings.



Crane operator Donald Leo, 30, died in the initial collpase Friday morning. Construction worker Ramadan Kurtij, 37, died Friday afternoon of cardiac arrest after being rushed to the hospital. Another construction worker remained critically injured, a city official said.



New York Mayor Michael Bloomberg said the cranes in the two incidents were different types.



"Two crane collapses in a short period of time look like a pattern, but there's no reason to think that there's any real connection," he said.



On a radio program Friday, Bloomberg vowed that an investigation would be conducted and changes would be made if necessary.



"I don't need any developer or union leader or anybody else telling me about the consequences of slowing things down," he said. "Nobody wants this economy to grow more than me. But we're not going to kill people."



The accident happened shortly after 8 a.m. Bridget Barrett, who lives two buildings away, said she was just leaving for work.



"We heard a loud crash as I was walking down my stairwell. I went to the front door of the building, and it was all white smoke everywhere," she said.



"The crane had fallen in the middle of the street and was on fire. There was water spewing out of the apartment building all over the place.  And I dialed 911."  See photos from the scene of the collapse »



Witnesses said the cab and the arm of the crane crashed more than 20 stories to the ground, smashing the penthouse on a building across the street and gouging chunks out of balconies all the way to the ground.



"It sounded like a large metal structure slowly falling on itself, sounded like a prolonged car accident," said iReport contributor Daniel Miranda, who lives a block away. "Construction workers were peering over the edge. Some of them were crying out in grief."



A pedestrian had minor injuries, Bloomberg said at a news conference, adding that nearby buildings with about 160 apartments were evacuated "strictly as a precaution."  Watch how latest crane collapse raises questions »



The collapse occurred a day after a building inspector rescinded a partial stop-work order that had been issued April 24.



The order was issued after an inspection found that employees had been working without a permit and operating a crane in an "unsafe manner," according to the city's Building Department. No other details were available.



The collapse left a pile of wreckage at the foot of the Azure, an apartment building under construction at the northwest corner of East 91st Street and First Avenue, a mainly residential area on the city's Upper East Side.



The falling crane also damaged the Electra, a 20-plus-story building on the southwest corner.  See where the crane fell »



Michael Schuman, another iReporter, said he heard a loud crash, grabbed his camera and went to the scene, about five buildings away.



"I got there before the emergency vehicles. It looked like the crane had broken into three or four large pieces. I saw water pouring out
How many remain critically injured? How many people remain critically injured? Who suspended all construction crane activity? What activity did the city suspend? What did the city suspend? How many were killed in the first accident? A previous crane collapse killed how many people? How many were killed in a similar accident? What killed the second construction worker? Where did a similar incident recently occur? What is the number of people that remain in critical injured status?
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question: How many remain critically injured?, answer: Another construction worker | question: How many people remain critically injured?, answer: 24 | question: Who suspended all construction crane activity?, answer: New York | question: What activity did the city suspend?, answer: construction crane | question: What did the city suspend?, answer: all construction crane activity | question: How many were killed in the first accident?, answer: two | question: A previous crane collapse killed how many people?, answer: Seven | question: How many were killed in a similar accident?, answer: Seven | question: What killed the second construction worker?, answer: a crane | question: Where did a similar incident recently occur?, answer: NEW YORK | question: What is the number of people that remain in critical injured status?, answer: 24