All four people onboard a small plane that crashed soon after taking off from London Southend airport on Sunday were killed, Essex police have confirmed.

The identities of the people have yet to be revealed but police said they believed all four were foreign nationals. Sky News reported that the victims included a woman from Chile and a male medical professional from an unknown European country. The pilot and co-pilot were reported to be Dutch. The plane was seen in flames with dark smoke billowing from it.

At a news conference outside the airport, Ch Supt Morgan Cronin, who is leading the investigation into the crash, said: “Shortly after takeoff, it got into difficulty and crashed within the airport boundary. Sadly, we can now confirm that all four people onboard died.

“We are working to officially confirm their identities. At this stage, we believe all four are foreign nationals. Our detectives and forensic teams are working in parallel with air accident investigators, the Royal Air Force, Essex fire and rescue service and London Southend airport to build an accurate picture of what happened.

“To aid our investigation, the Civil Aviation Authority has put in place a significant air exclusion zone surrounding the crash site. We’re also speaking with dozens of witnesses, some of whom have already provided video footage, and we’d like to thank them for their help.”

Lisa Fitzsimons, a senior inspector at the Air Accidents Investigation Branch, said it was too early to speculate on the cause of the crash.

“Our investigation is in parallel to the investigation by Essex police. If there are safety lessons that can be learned, we will make recommendations that aim to prevent a similar accident occurring,” she said

“The aircraft involved in the accident was a Beechcraft B200 Super King Air. As part of our investigation, we are liaising with other state investigation authorities. Our focus is on gathering the physical evidence from the accident site and interviewing witnesses.

“The remains of the aircraft will then be recovered to our facility in Farnborough, Hampshire for further detailed investigation … Our thoughts are with the families and friends of everyone involved.”

The chief executive of Southend airport, Jude Winstanley, said the facility would remained closed until further notice. Dozens of flights have been cancelled or rerouted. Winstanley said affected passengers should contact their airline for advice.

The East of England ambulance service said it dispatched four ambulances, a rapid response vehicle, four hazardous area response team vehicles, three senior paramedic cars and Essex and Herts air ambulance to the scene on Sunday. Essex county fire and rescue service said four crews along with off-road vehicles attended the incident.

The aircraft, operated by Zeusch Aviation, was equipped with medical systems for transporting patients. The Dutch company specialises in medical evacuations and transplant flights and also runs private charters.

The airline confirmed its flight SUZ1 had been involved in an accident. “We are actively supporting the authorities with the investigation and will provide updates as more information becomes available,” it said. “Our thoughts are with everyone who has been affected.”

It is unclear whether the flight was a medical evacuation or whether any patient was onboard.

According to the flight-tracking service Flightradar24, the plane took off at 3.48pm and was bound for Lelystad, a city in the Netherlands.

John Johnson, from Billericay, was at Southend airport with his family at the time of the crash. He told PA Media: “We all waved at the pilots and they all waved back at us. The aircraft then turned 180 degrees to face its takeoff departure, powered up, rolled down the runway.

“It took off and about three or four seconds after taking off it started to bank heavily to its left, and then within a few seconds of that happening, it more or less inverted and crashed just headfirst into the ground. There was a big fireball. Obviously, everybody was in shock in terms of witnessing it. All the kids saw it and the families saw it.”

EasyJet earlier said all of its flights to and from Southend had been “diverted to alternative airports or are no longer able to operate”.