Officials are investigating what caused an Amazon cargo plane to overshoot the runway after landing at Miami International Airport in a deadly incident on Sunday.

Five people were killed and five others seriously injured when the plane, which was operated by 21 Air, crashed just before 14:00 (18:00 GMT). None of the group have yet been identified.

The plane, a Boeing 767-300, crossed a road beyond the runway and hit several vehicles on the ground. It is not yet clear whether those who died were in the aircraft, on the ground, or both.

21 Air, a charter company based in North Carolina, said it was "devastated by the accident involving one of our aircraft in Miami".

Both 21 Air and Amazon said they were co-operating with the investigation.

"At least five people have lost their lives, and five others are injured," Miami-Dade County Mayor Daniella Levine Cava said at a news conference on Sunday evening.

She added that rescue crews arrived at the scene within "seconds" of the crash.

Three of the five people injured were in critical condition, Miami Fire Chief Raied Jadallah said.

Several of the injured were trapped inside or under vehicles on the ground, and needed to be extricated by fire and rescue crews, Jadallah added.

Over 200 firefighters responded after the plane burst into flames.

Officials say it is too early to know the cause of the crash, which is being investigated by the National Transportation Safety Board (NTSB).

The federal agency, which investigates all air crashes in the US, plans to hold a news conference of its own on Monday.

Experts who spoke to the Associated Press news agency said video footage of the plane's landing would present investigators with the question of whether or not the aircraft touched down within its designated zone on the runway - and if so, what happened.

All flights at the airport were temporarily grounded by the Federal Aviation Administration (FAA). The incident came over Labor Day weekend, one of the busiest travel times of the year.

Locals have described the aftermath of the incident. One woman, Beth Tilman, told the New York Times said she had seen a black cloud where the plane had crashed, and had smelled an acrid stench.

"It wasn't trees burning. It wasn't mangroves burning. It was some other odour that I, honestly, had never smelled before," she said.

A student pilot, Rohan Ellis, told the same newspaper he had witnessed sirens and helicopters overhead when he arrived at the scene of the crash. Describing what had happened to the vehicles that the plane had hit, he said: "They were mangled."

Flight data from tracking site FlightRadar24 shows that the Amazon cargo flight was travelling at 112 knots (129mph, 207km/h) as it exited the "useable runway".

In a blog post, the site said the plane came to rest near a car park that serves an Amazon warehouse and other businesses.

There were light thunderstorms and gusting winds in Miami at the time of the incident, the site says.

Kelly Nantel, Amazon's Director of Corporate Global Media Relations, said: "We're heartbroken to learn that five people lost their lives in today's incident at Miami International Airport.

"Our deepest sympathies go out to the families, loved ones, and all those affected by this devastating loss.

"The airplane, which was operated by 21 Air, was attempting to land when this incident occurred. We're working closely with local authorities and officials to learn more and will co-operate fully with any investigation."

The statement from 21 Air's CEO Keith Winters said: "Our deepest condolences are with the families and loved ones of those who lost their lives.

"Our immediate priorities are supporting those affected, assisting the authorities, and ensuring that accurate information is communicated as it becomes available."

The plane had earlier departed Luis Muñoz Marín International Airport in San Juan, Puerto Rico.

The crash comes during one of the busiest travel weekends of the year in the US.

Passengers at the airport told the BBC they were frustrated by the lack of information coming from officials, with many flights cancelled or delayed as a result of the incident.

There were long queues at airline counters as people tried to reschedule travel plans, with some saying they would be forced to stay in Miami an extra night.

"The earliest I could find to fly to San Francisco was Tuesday morning," said one traveller named Faroush. "I'll probably have to find a hotel and spend more time in Miami."

The Transportation Safety Administration (TSA) said there would be 17 million travellers passing through US airports in the week leading up to Monday's Labor Day holiday.

The TSA, which screens passengers flying in the US, predicted that 2.3 million people would fly on Sunday alone.

Miami International Airport (MIA) is located near downtown Miami, and is one of the busiest airports in the country.

"Founded in 1928, MIA is America's busiest airport for international freight and second busiest for international passengers, offers more flights to Latin America and the Caribbean than any other US airport," according to its website.

About 60% of all international visitors to Florida arrive at this airport, it says.