The wife of Orlando gunman Omar Mateen was with him when he purchased ammunition used in the deadly assault on a gay nightclub, and attempted to talk her husband out of launching an attack, according to reports.

Noor Zahi Salman, who was married to Mateen for three years and had a young son with him, told the FBI that she once also drove her husband to Pulse nightclub in downtown Orlando because he wanted to scope it out, NBC News in the US reported, citing law enforcement officials.

Officials are investigating whether Ms Salman, 30, had any prior knowledge of her husband's plan to attack and kill patrons at the nightclub, where he went on a rampage in the early hours of Sunday morning, killing 49 people and wounding 53 others, before he was shot dead by police.

If Ms Salman knew of her husband's intent but did not report it to authorities, she could face criminal charges, the unnamed law enforcement officials told NBC News.

Mateen purchased a Glock handgun and an AR-15-type semiautomatic rifle during two separate visits this month to the St Lucie Shooting Centre, several kilometres from PGA Village, a gated community where he worked as a security guard.

Ms Salman told the FBI she was with him when he bought ammunition and a holster. Ms Salman has not made any public statements about her husband since the shooting.

Ms Salman is said to be cooperating fully with investigators, and no decision has been made about whether she will be charged.

A senior law enforcement official told the New York Times that there was "an indication that she [Ms Salman] was with him [Mateen] in certain parts of the process, and we're sorting through it".

The Orlando Sentinel reported that police escorted Ms Salman back to the apartment she shared with Mateen in Fort Pierce on Tuesday, local time.

Fort Pierce police spokesman Ed Cunningham said that police also were investigating a reported burglary at the house following the shooting. He said the FBI left the home secured at 5am on Monday. At 10am the same day, police received a call from reporters to say the apartment's back door was open.

Meantime, the Orlando Sentinel reported that Mateen had visited a number of Disney properties in recent months, and was most recently spotted early in June in Disney Springs, an outdoor shopping and entertainment complex in Walt Disney World in Orlando.

That visit may have overlapped with Gay Days Orlando, an annual event that brings thousands of LGBT people to central Florida, the newspaper reported, citing a US law enforcement official briefed on the investigation.

Another US official said that the Walt Disney Company had provided information to the FBI that made it clear that Mateen was "not simply acting as a tourist" during a visit to Walt Disney World two or three months ago.

Disney has raised security at its theme parks following the nightclub shooting. It also has donated $US1 million ($1.36 million) to a fund established by the mayor of Orlando to help those affected by the mass shooting, and will match additional donations from Disney employees dollar-for-dollar.