A massive fire at a large residential construction site early Tuesday in West Oakland — the East Bay’s sixth major conflagration at a housing development in a little more than two years — has renewed concerns that a serial arsonist is targeting projects across the region.

That suspicion was fueled by a second discovery Tuesday morning: a gas can, rag, match, hammer and the remnants of an intentionally set fire that burned itself out 10 blocks away at an under-construction apartment complex not far from the Oakland-Emeryville border.

Oakland and nearby cities have been on high alert ever since video footage captured a hooded bicyclist sneaking past two security guards and a network of cameras to ignite a blaze that leveled a $35 million Emeryville residential complex in May 2017— the second time that site was targeted in 10 months.

In April of this year, surveillance cameras captured a hooded arsonist in Concord scaling a fence to start a $55 million blaze before making off in the night. That fire required 250 people to be evacuated from nearby apartments.

The series of fires has sent developers scrambling to ramp up security to protect their projects, and has fueled speculation that the attacks have been motivated by anger at rising housing costs and gentrification.

“We feel this is the act of a cowardly urban terrorist, an individual or group of individuals that come by and torch these buildings in the middle of the night,” said Greg McConnell, head of the Jobs & Housing Coalition, a group of large Oakland developers.

The blazes have disturbed developers and elected officials, but they’ve also terrified neighbors who’ve awakened in the middle of the night to sirens or someone banging at their doors and telling them to get out.

“Yes, I’m irritated,” said Cindy Davis, 57, who was awakened at 2 a.m. to find a sky full of flaming embers, one of which ignited a small fire that charred the corner of her roof.

Tuesday’s blaze at West Grand Avenue and Filbert Street was the second time that site has caught fire, according to an email obtained by The Chronicle.

A smaller fire on April 29 was quickly extinguished, but it prompted a senior Fire Department official to warn superiors that the site was so poorly secured it was at risk of becoming a “total loss.” Six of the property’s nine buildings were destroyed Tuesday.

Mayor Libby Schaaf stopped short of calling the destructive fire on West Grand a case of arson, but she hinted at other fires that have incinerated developments in Oakland, Emeryville and Concord.

“We are calling on everyone to be vigilant, to look out for this needed construction of housing and ensure that it’s built safely,” Schaaf said. “We call on everyone who lives around construction sites to monitor those sites, to call 911 if they see anything suspicious.”

She added: “An attack on new housing in Oakland is an attack on keeping families housed in Oakland.”

Reports of Tuesday’s three-story-complex fire came in around 1:59 a.m., said Nick Luby, a deputy fire chief with the Oakland Fire Department.

“It’s just a big pile of kindling,” Luby said of the construction site. “Small timber, it just grows quite quickly.”

Investigators from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were assisting Oakland firefighters in their investigation of the blaze.

An email shows investigators were previously aware of a small fire reported at the site April 29 in a first-floor stairwell of Ice House, a development of all-electric townhomes. The missive raised alarms about the lack of security cameras, a lone security guard and the lack of secure fencing to keep out intruders and squatters.

Fire Chief Darin White acknowledged Tuesday that a fire had taken place at the project in April, but he said he was unaware of anyone expressing security concerns about the property.

Phil Kerr, CEO of City Ventures, the project’s developer, also confirmed the April fire. He said security cameras were installed six months ago but did not say whether it was in response to the fire official’s concerns.

Kerr said just one security guard was on site Tuesday morning but that he will triple that along with completing a full security assessment for the site. He said the fire, regardless of the cause, will not stop construction of the project. Fifty of the units have been sold, he said, and families were prepared to move in before the end of the year.

“We’re resolute,” Kerr said. “We’ll continue to work toward building the homes that we set out to build.”

Four of the six buildings burned Tuesday were in the early stages of construction and completely destroyed, Luby said. A firefighter who suffered a leg injury while battling the blaze was taken to the hospital and listed in stable condition. A total of 90 firefighters responded.

Nearly 30 residents in nearby homes were evacuated, and Pacific Gas & Electric Co. shut off power in the area due to the threat of flames reaching power lines and transformers, Luby said, leaving 2,000 people without power.

Flying embers filled the early-morning sky, and ignited a nearby home on the 3600 block of Isabella Street.

“I came outside and the whole sky was raining fire,” Davis said. “The corner of my roof caught fire from the falling debris. To see fire coming out of the sky like that, it was unbelievable.”

The fires on her roof, and a home down the street, were quickly contained.

Jessica Molina, 20, woke up about 2 a.m. to a woman’s screams outside her home warning neighbors of a fire.

“When I woke up, I was just like, ‘Whoa, what happened,’” Molina said, clutching her black Maltese-mix dog, Snickers. “Hearing that in the middle of the night was kind of scary, especially for the little ones and my dog.”

Crews responding to a nearby home that started smoking due to flying embers pic.twitter.com/pORbbJTCQ9 — Sarah Ravani (@SarRavani) October 23, 2018

Twenty-two condos were expected to be ready by a December move-in date, and a total of 126 units were expected to be completed within a year and a half, according to the website for developer City Ventures.

In addition to a security guard, City Ventures had 15 security cameras live-streaming when the fire occurred, officials said. Developers across the East Bay have started equipping their projects with video cameras, heat and motion detectors, tall fencing, alarms, bright lights and 24-hour security guards, officials said. Some developers have also started using fire-retardant products

The Jobs and Housing Coalition said in July that members have quadrupled their spending on security since the blazes that occurred at developments in Oakland, Emeryville and Concord.

McConnell, the coalition’s chief executive officer, said Tuesday that some developers are spending as much as $60,000 a month to secure individual construction sites.

The group has offered a $300,000 reward for information leading to the arrest of residential construction site arsonists in Oakland and Emeryville.

Schaaf urged residents with information to call the city’s anonymous arson tip line at 510-238-4031.

San Francisco Chronicle staff writer Kimberly Veklerov contributed to this report.

Sarah Ravani and Michael Cabanatuan are San Francisco Chronicle staff writers. Email: sravani@sfchronicle.com, mcabanatuan@sfchronicle.com Twitter: @SarRavani, @ctuan