Fire and Emergency New Zealand is asking Southlanders to think before they light fireworks tonight after seven fires around the country in the first two days of retail sales were put down to fireworks.

In a statement on Wednesday the agency said three vegetation fires on Monday, in Papatoetoe, Kawerau and Fernside, and three more on Tuesday, in Rangitaiki, Ferrymead and Seddon, along with a car fire in Rangiora, were all probably caused by fireworks. None was in Southland or Otago.

Tom Ronaldson, the agency's acting national manager for community readiness and recovery, said there had been fewer fireworks fires so far than in previous years, but that every one of them could have been avoided. Fireworks fires had risen over the past two years, he said, and the agency wanted that trend turned around. "Low risk doesn't mean no risk," he said.

Fireworks can only be sold from 2 to 5 November each year, so tonight is the last night of sales as well as Guy Fawkes itself. They can be let off at any time of year.

The weather may do some of the fire service's work for it. MetService said on Thursday that the west and south of the South Island, Southland included, would see rain moving in during Thursday afternoon and into the evening, with the north-east of the island keeping more of its sunshine. Meteorologist Alanna Burrows said conditions should not cause too much trouble for displays in the main centres, with light northerly winds, but pockets of high and very high fire danger remained around the country.

MetService also flagged a thunderstorm risk building over inland parts of the country on Friday and Saturday, and said parts of the South Island could be affected as the weekend, and election day, approached.

Southland's recent record shows why the agency is cautious. A high-country fire at Centre Hill, north of Mossburn, burned through about 130 hectares late last month before rain helped crews bring it under control, and a 600-metre scrub fire on the Ōreti Beach dunes in August was treated as suspicious.

Fire and Emergency's advice for tonight is straightforward. Look up the fire danger and any restrictions for your area on checkitsalright.nz first, and ask the council before using a beach or park, as many public spaces have year-round fireworks bans. Do not set fireworks off in wind. Keep a bucket of water or a hose within reach, aim fireworks at the sky and away from buildings and trees, and let neighbours know in advance, particularly anyone with pets or livestock. Spent fireworks should be soaked in water before they go in the bin.

Southland's rural fire season status is set by Fire and Emergency and can change at short notice; the agency's checkitsalright.nz site carries the current setting for each district. If a fire gets away, call 111.