KQED News staffers Lisa Pickoff-White, Olivia Allen-Price, Charla Bear, Mina Kim, David Weir, Jeremy Raff, Mark Andrew Boyer, Pat Yollin, Joanne Elgart-Jennings and others contributed to this report.

Firefighters work to contain a five-alarm fire at Fourth and China Basin streets in Mission Bay. (Charla Bear/KQED) — Firefighters work to contain a five-alarm fire in China Basin. (Charla Bear/KQED)

Update 9:10 a.m. Wednesday: San Francisco firefighters continue to pour water on the site of Tuesday's five-alarm Mission Bay fire, as arson investigators search for the cause of the blaze that destroyed a 172-unit apartment building under construction.

Fire Department spokeswoman Mindy Talmadge said investigators had determined welding was going on at the site and ended between 3:30 p.m. and 4 p.m., about an hour before the fire was reported. "The investigation is ongoing, but it's leaning in the direction of an accidental fire," Talmadge said.

About 10 fire rigs and 35 firefighters are still stationed around the burned building, part of a two-building complex on the west side of Fourth Street between Mission Rock and China Basin streets. At the height of the fire Tuesday evening, half of the roughly 320 firefighters on duty in the city were fighting the blaze. Talmadge said crews will stay on the scene until they determine it's safe for engineers to assess the building for demolition.

The Fire Department reports two injuries in the blaze: a firefighter, one of the first on the scene, who suffered first- and second-degree burns to the face and hands, and a battalion chief who sprained an ankle.

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A 190-unit apartment building directly across Fourth Street from the fire remained evacuated Wednesday morning. Searing heat from the fire blew out windows in 30 units facing the blaze, triggering sprinklers.

The destroyed structure was part of a two-building, 360-unit development. Developer BRE Properties said the second building was not affected by the fires, and construction crews were back at work there Wednesday.

Update 8:45 p.m. Tuesday: KCBS reporter Chris Filippi reports the first injury in the Mission Bay blaze: One of the first firefighters on the scene after the fire broke out around 5 p.m. is reported to have suffered burns to his face and hands. Filippi says the unidentified firefighter stayed on the line for hours before "copping to" his injuries and being sent to San Francisco General Hospital for treatment.

Update 7:51 p.m.: San Francisco Fire Chief Joanne Hayes-White says fire crews are getting the upper hand on the blaze, and have saved the surrounding buildings.

Hayes-White said that firefighters will be on the scene through the night. Streets around the fire will be closed through Wednesday, and possibly into the week as crews work to safely bring the remains of the building down.

The apartment complex is very precarious, KQED's Charla Bear reports. Parts of the building have already collapsed internally, and the top portion of the building is leaning to one side.

Update 7:31 p.m.: Crews have been unable to get into the structure and determine the cause of the fire.

"There's concerns about getting into where we can get in because it's going to be vulnerable," Hayes-White. "We have a joint fire and police arson task force. They'll have to determine cause and origin. We'll talk to the contractors, whether it's welding or — we don't know. We have no idea."

Hayes-White said that firefighters will be on the scene through the night. Streets around the fire will be closed through Wednesday and possibly into the week as the building comes down.

The building is very precarious, and the top portion of the building is leaning to one side. Parts of the building have already collapsed.

Update 6:55 p.m.: At the time, Hayes-White said it would take hours to contain the fire. More than 150 firefighters and about 85-90 apparatus are currently working.

Workers had gotten off around 3:30 or 4 p.m, the fire chief said, and the fire had about an hour to smolder.

"It went up very quickly once it started," she said, because there was no fire protection installed yet in the building.

Hayes-White described the blaze as "pretty significant" saying it had been years since there was a five-alarm conflagration in the city. She said it helped to look at previous fires the department had helped fight, especially the massive 2002 blaze at Santana Row in San Jose.

Firefighters evacuated people in buildings down to Third Street.

Update 6:41 p.m.: Firefighters put a fire curtain to help contain the blaze. There was a small fire that spread to a nearby building but it was contained, Hayes-White said at a press conference.

Winds could have made the fire much worse. Starting at 8 p.m. tonight, the National Weather Service has issued a wind advisory, with gusts that could go up to 40 mph.

Update 6:25 p.m.: Firefighters are battling a five-alarm blaze at Fourth and China Basin streets. The building has begun to collapse. KPIX is reporting that the fire has spread to the roof of a building at UCSF's Mission Bay campus.

Mindy Talmadge, a spokeswoman for the San Francisco Fire Department, says the building was under construction, which makes battling the blaze more difficult because the building's fire suppression systems had not yet been installed.

"The glass on the building across the street is starting to fail from the heat," said Talmadge.

The future complex is located across the street from the Strata at Mission Bay apartments, according to a spokeswoman for the Sares Regis Group, which manages that property. Channel 5 reported that BRE Properties was due to complete the work shortly and that each of the units in the nine-story, $227 million complex was going to sell for $630,000. The sprinklers were not functional yet.

Update 5:35 p.m.: The fire was reported at at 4:56 p.m. today. Crews arrived on the scene at 5:04 p.m.

"There's a tremendous plume of smoke that goes across the sky," said KQED's Mark Andrew Boyer. KCBS reports that the smoke column has risen to more than 3,000 feet.

The sun sets, highlighting the smoke from the 5-alarm fire. (Jeremy Raff/KQED) — The sun sets, highlighting the smoke from the five-alarm fire. (Jeremy Raff/KQED)

Fourth and China Basin fire. (Mark Andrew Boyer/KQED) — Fourth Street and China Basin fire. (Mark Andrew Boyer/KQED)

People watch the China Basin fire from afar. (Jeremy Raff/KQED)

Firefighters pour water over a five-alarm fire in China Basin. (Charla Bear/KQED)

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KQED's Joanne Elgart-Jennings took a video.
[youtube http://www.youtube.com/watch?v=mpyx4iaXYfs]

Firefighters cross over Channel Street. (Jeremy Raff/KQED)

Fire at Fourth Street and China Basin. (Mark Andrew Boyer/KQED) — Firefighters begin to contain the fire. (Mark Andrew Boyer/KQED)

[View the story "4-Alarm Fire Near AT&T Park" on Storify]

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