Thick black smoke was still rising in the sky, soot covered the streets and cars, balconies filled with black gunk, and the toxic air had filled the lungs as Tehran woke up after a night of airstrikes on the city’s oil depots on Sunday.

In messages and voice notes sent to the Guardian, people described the situation in their homes and on the streets, some calling it “apocalyptic”. With the sun blotted out, disoriented people in Iran’s capital had to turn on their lights to see through the gloom.

Four oil depots and a petroleum logistics site in and around Tehran were hit. Local authorities said six people were killed and 20 wounded at one of the sites.

Videos shared by citizen journalists showed massive flames over the Tehran sky overnight and smoke still billowing over the oil storage facilities. As rain poured down on the city of 10 million people on Sunday morning, authorities warned of toxic acid rain and many residents woke up with pain in their throat and eyes burning.

Speaking to the Guardian via voice notes, Negin – not her real name – an activist and former political prisoner based in the central-east side of the city, said the situation was “apocalyptic”.

She said: “The situation is so frightening it’s hard to describe. Smoke has covered the entire city. I have severe shortness of breath and burning in my eyes and throat, and many others feel the same. But people still have to go outside because they have no choice. Many places reopened today, but closed again because it’s impossible to stay outdoors.”

Iran’s environmental agency advised people in Tehran to stay indoors. The country’s Red Crescent said the toxic chemicals could lead to acid rain and hurt the skin and lungs, advising people to avoid turning on air conditioners or going outside immediately after rainfall. It also encouraged people to protect exposed food. Tehran’s governor recommended wearing masks outside. Dr Shahram Kordasti, a UK-based Iranian haemato-oncologist, warned the toxic gases and fine particulate matter could irritate the eyes and airways, worsen asthma, pulmonary conditions and heart disease, and increase the risk of some cancers.

Negin, who went out to buy a mask and an inhaler, said: “Even masks are becoming difficult to find. This is a huge mistake. I ask those who have the ability, especially foreign media, to reflect on this situation. What are people supposed to do under these conditions? This is truly a crime against humanity.”

Speaking about the effects on people of the US-Israeli strikes continuing around her she said, “This is no longer just a human rights violation. It is truly anti-human behaviour. If someone has a problem with the Islamic Republic government, that is one thing – but not with us, the people. You cannot attack water systems or refineries. Most of Tehran’s water comes from dams. If those become polluted, what happens then? The government has basically left people on their own.”

She said: “Prices are skyrocketing. I bought an inhaler for 850,000 tomans [£4.50]. Where are people supposed to get this money? Many people in Tehran are daily workers who haven’t had work for a long time. Food is becoming extremely expensive, and many things are becoming scarce.”

For Negin, who decided to stay in the city, there was a feeling of helplessness. “The pressure inside the country is becoming enormous. There are shortages of basic goods. There was no gasoline anywhere. Today in many places they are giving people only five litres of fuel. The situation is extremely painful.”

In other messages relayed via relatives abroad, two Tehranis said everyone was advised to stay indoors and given instructions on domestic media on how to deal with the toxic air and keep safe.

Mehdi – speaking under an alias – is a 42-year-old restaurant owner who lives in the west of the city. He said the fear of inhaling the toxic gas and touching anything is similar to how it felt during Covid. “We are so scared to even clean the windows and balconies. There’s soot everywhere and we don’t even want to touch it with gloves. My eyes are burning and I look outside and see people without masks are going on with their daily lives. I am not so brave. There’s this smell in the air I can’t explain.”

Mehdi said he also planned to leave the city and that it would be hazardous to serve people food in his restaurant until he knew the water was safe. “Trust me, we are on our own. This regime doesn’t care about us so why would I make a plea to a foreign power to care for us? And tell those saying we asked for this. No! We didn’t ask for the death of our people who were getting killed by the regime anyway. And if you haven’t cared when they gunned us down, zip your mouth now. We [Tehranis] are here to help each other even if this government doesn’t.”

As Israel targeted the oil storage facilities on Saturday evening, Mehnaz, 39, who did not want her real name published, tried to flee the south of the capital, she said in messages. Believing the strikes would get worse early the next morning, she and her husband packed up essentials and got in the car. After driving just a few minutes, she saw bright flames in the sky towards the Shahr-e Rey oil depot.

Thinking it was just another explosion, she drove ahead, not realising the oil depot had been hit. The internet shutdown imposed by the regime meant she had no information on what was hit and where. “I thought leaving now was safe because they will hit early [on Sunday] morning, but I had to come back,” she said.

At about midnight on Saturday, she wrote: “Tehran is burning. And smoke has filled the streets. It’s impossible to drive out of the city right now and even with the windows closed, heavy smoke is making its way inside … [I am] clueless whether to stay in or brave the flames and drive out while it’s still on fire. I don’t even have a mask.”

But on Sunday, Mehnaz decided staying put in the city was no longer feasible. She fled at about 11.30am and drove towards her parents’ home outside the province.

“There was a long queue for gas and they were rationing and putting a limit on how much we [could] fill in,” she said. “The Rey depot, you won’t believe, was still on fire and it’s insane because in the night it looked like day and in the day, it was so dark, it looked like a new moon night. So, so dark, just like our futures.”

She said: “While I was leaving I noticed there wasn’t a single bird in the sky and you know what they say? When the birds abandon you, you are truly on your own. We have so many cats in the city. If these attacks continue, whoever rules here next, they will rule over a democracy of cats. But then even cats have only nine lives.”

Additional reporting by Angelique Chrisafis, Associated Press and AFP