A suspect being hunted over the Manhattan and New Jersey bombings is in custody after a shootout.

Ahmad Khan Rahami (28), a naturalised US citizen from Afghanistan who had been described as "armed and dangerous" by the FBI, was injured in the gun battle with police.

In video footage, he was shown on a stretcher being taken into an ambulance, with a bloodied bandage on his right arm and moving his head from side to side with his eyes open.

The suspect was sleeping in the doorway of a bar when the owner reported him to police and an officer went to investigate and recognised him as Rahami.

Police said the man pulled out a gun and shot the officer, who was wearing a bullet-proof vest, in the chest and then a shootout erupted with other officers before Rahami was captured.

A second officer was injured in the hand in the gun battle in Linden, New Jersey. Both are expected to recover.

Rahami, who was not on US anti-terrorism databases, was later having surgery on his leg following a gunshot wound.

Authorities are currently not looking for anyone else over the bombings and do not believe he was part of a wider cell.

Speaking after the suspect's arrest, New York Mayor Bill de Blasio said they now "have every reason to believe this was an act of terror".

The development in the fast-moving investigation came after five devices were discovered in nearby Elizabeth, one of which exploded as a bomb squad robot tried to disable it.

FBI agents raided an apartment linked to New Jersey resident Rahami above a fried chicken outlet in Elizabeth, close to where the devices were found late on Sunday.

The discovery followed a series of attacks in the US over the weekend.

29 people were injured in a bomb blast in the busy Chelsea district of Manhattan on Saturday evening.

Earlier there had been an explosion in nearby New Jersey, and there was also a knife attack in Minnesota later that day, which wounded eight.

The authorities have now linked the explosive devices in both New York and New Jersey but President Barack Obama said they do not appear to be connected to the Minnesota stabbing.

People watch in the rain as police and officials gather at an apartment building in Elizabeth, N.J. Image: Mel Evans / AP/Press Association Images

In a speech this afternoon, President Obama said he wanted to commend "all the outstanding police and first responders in both New York City and New Jersey.

"The investigation is moving rapidly, and as is my practice I am going to leave it to the FBI and law enforcement to provide details," he added.

He also called on American people to not succumb to fear.

"We all have a role to play as citizens in making sure we don't succumb to that fear - and there's no better example than the people in New York and New Jersey."

Meanwhile, New York governor Andrew Cuomo, having previously ruled out a link between the Manhattan bombing and international terrorism, has now acknowledged "it may be foreign related".

Five men had already been detained and questioned over Saturday's bomb attack in Chelsea, after the FBI stopped "a vehicle of interest" in Brooklyn on Sunday night.

It has been reported the bomb that detonated in Manhattan, and a second unexploded device, were both shrapnel-filled pressure cookers, similar to those used in the attack on the Boston Marathon in 2013.

The string of attacks began on Saturday morning after a small pipe bomb exploded in the New Jersey town of Seaside Park, shortly before a charity run for US marines and sailors. No one was injured.

The devices in Elizabeth, which were left in a bin, were discovered after two men "saw wires and a pipe".

The security alert came as nearly 1,000 extra police were deployed on New York's streets as world leaders met for a UN summit on the refugee crisis.

US attacks timeline:

• Saturday morning - pipe bomb explodes on the route of a New Jersey charity run in aid of US marines and sailors
• A man stabs eight people at a shopping centre in Minnesota before being shot dead
• An explosion in Manhattan injures 29 people on Saturday night. Police find a second unexploded device nearby
• Sunday night - a backpack containing five devices is found in a bin near a train station in the New Jersey city of Elizabeth
• Monday morning - One of the devices explodes as bomb squad robots attempted to disable it in the early hours